threshold

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is spelt with one h (contrast withhold), and the h is optionally silent or aspirated in speech.

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The point at which a signal (voltage, current, etc.) is perceived as valid.

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noun

A transitional interval beyond which some new action or different state of affairs is likely to begin or occur: borderline, brink, edge, point, verge. See edge/center.

A threshold is the exposure level or dose of an agent above which toxicity or adverse health effects can occur, and below which toxicity or adverse health effects are unlikely. For example, taking aspirin is therapeutic and not dangerous up to a contain dose, but above that dose it can cause nausea, brain damage, bleeding, and, eventually, death. Sulfuric acid is not dangerous when only small amounts of it get on a person's skin, but if the amount gets too high, it burns. Thresholds for toxicity exist because, up to a certain point, the body can repair damage and detoxify chemicals to which it is exposed. If the exposures get too high, however, the detoxification and repair mechanisms are overwhelmed and toxicity starts to occur.

Thresholds for toxicity can be different in different people, with some people likely to be sensitive to smaller levels of exposures than others. In other words, toxicity thresholds are distributed differently within a population. For example, some people can breathe a lot of paint stripper without feeling ill, while others get sick from it quite easily. So while it may be easy to demonstrate a chemical's threshold for toxicity in identical laboratory animals, a threshold for toxicity in a diverse human population may be very difficult to determine.

The concept of a threshold for toxicity has played an important role in chemical regulation. Until recently, chemicals that cause cancer were assumed to have no threshold for their effects, while chemicals that cause other kinds of health effects were assumed to have thresholds. It is now known that some cancer-causing chemicals have thresholds and some other toxic agents do not, and this knowledge is slowly making its way into regulatory guidelines.

An example of a nonregulatory guideline that is based on toxicity thresholds is the threshold limit value (TLV). TLVs were derived as chemical exposure levels that are permissible in the workplaces—if workplace exposures stay below the TLVs, workers are unlikely to be adversely affected. TLVs were established first in 1968 by a nongovernmental organization known as the American Conference of Governmental Industrial Hygienists (ACGIH) based on available scientific information and best professional judgment. The ACGIH TLV Committee periodically reevaluates and updates the TLVs, based on professional judgment and new scientific information, but it uses no explicit risk-based or feasibility-based methodology. When the Occupational Safety and Health Act was enacted in 1970, the new Occupational Safety and Health Administration adopted existing TLVs as workplace permissible exposure limits (PELs).

(SEE ALSO: Carcinogen; Exposure Assessment; Herbicides; National Institute for Occupational Safety and Health; Occupational Safety and Health Administration; Pesticides; Regulatory Authority; Risk Assessment, Risk Management; Toxicology)

Bibliography

Aldridge, W. N. (1986). "The Biological Basis and Measurement of Thresholds." Annual Review of Pharmacology and Toxicology 26:39–58.

—— (1995). "Defining Thresholds in Occupational and Environmental Toxicology." Toxicology Letters 77:109–118.

American Conference of Governmental Industrial Hygienists (ACGIH) (2001). Documentation of the Threshold Limit Values and Biological Exposure Indices, 7th edition. Cincinnati, OH: Author.

Ottoboni, M. A. (1997). The Dose Makes the Poison: A Plain Language Guide to Toxicology, 2nd edition. New York: Van Nostrand Reinhold Co.

— GAIL CHARNLEY

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1. the beginning of that portion of the runway usable for landing.

2. the point at which military operations transition from one level to another, for example, a nuclear threshold is that point at which the transition from the use of conventional weapons to the use of nuclear weapons takes place.

See the Introduction, Abbreviations and Pronunciation for further details.

Symbolically, a threshold marks the boundary between a household and the outer world, and hence between belonging and not-belonging, and between safety and danger. Guarding the doorway is an important aspect of magical house protection, which can involve the threshold. In Tudor and Stuart times this (rather than the door itself) was the usual place to fix horseshoes, and in some cases the threshold itself was an iron slab (C. F. Tebbutt, Folklore 91 (1980), 240). Later, there was a custom in some areas of making patterns on well-scrubbed doorsteps, which some people regarded as simply decorative, but others as defensive. Thus, in Herefordshire a pattern of nine crosses kept witches out (Leather, 1912:18), and up to about 1900 every Shropshire farmhouse and cottage had its doorstep and hearthstone decorated with patterns made from the pigment produced by squeezing elder or dock leaves, and some still did in the 1930s.

[They] are for the most part very simple—a border of crosses between two lines; a series of vandykes with or without a circle in the wide part of each vandyke; two large crosses, divided by a vertical line.… I can remember that when I was a child, one of our maids used to decorate the back doorstep with a border of loops, and it is an interesting point that these loops had to be done straight round in an unbroken chain. It would have been ‘unlucky’ to do the top of the step and then break off and do the bottom of it before the sides. … These patterns were said to keep the Devil away. … Nowadays they say the patterns are ‘laid’ for luck; or a young woman may say that she does them to ‘plaze granny, who dotes on 'em, bein' as they've allus bin laid 'ere’. (L. H. Hayward, Folk-Lore 49 (1938), 236-7)

1. A strip fastened to the floor beneath a door, usually required to cover the joint where two types of floor material meet; may provide weather protection at exterior doors. Also See doorsill.
2. In illumination engineering, the value of physical stimulus which permits an object to be seen a specified percentage of the time with specified accuracy.

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Threshold (1957- ), a literary magazine founded in connection with the Lyric Players Theatre and edited at first by Mary O'Malley with John Hewitt as poetry editor.

limen

A term that usually refers to the weakest value of any stimulus or other agency that will produce a specified effect. This is sometimes called the absolute threshold or stimulus threshold. The term may also refer to the smallest difference between two stimuli (the just-noticeable difference), in intensity, magnitude, or pitch, which can be discriminated. This is more precisely referred to as the difference threshold or differential threshold. The terminal threshold is the upper limit of sensitivity; the point beyond which further increases in the intensity of stimulation have no typical effect. For example, increases of light intensity above the terminal threshold may cause pain, but this is not the usual effect of that stimulation.

(DOD, NATO) The beginning of that portion of the runway usable for landing.

A threshold is a symbol for passing from one state or condition to the next, indicating a transition in some aspect of the dreamer's life.

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The beginning of that portion of the runway usable for landing (ICAO). On instrument runways, it is indicated by long stripes followed by the runway designation marking. The number of stripes is dependent on the width of the runway.

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the value that must be achieved or exceeded for an effect to become discernible. For example, the kidney threshold of excretion, for any substance, is the plasma concentration at which not all of the substance that appears in the filtrate can be reabsorbed, so that it appears in the urine.

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The level that must be reached for an effect to be produced, as the degree of intensity of stimulus which just produces a sensation.

• t. phenomenon — a theory explaining pruritus which states that some degree of pruritus is tolerated by a patient, but a small increase from an additional source raises the patient above their threshold and causes clinical signs.
• renal t. — that concentration of a substance in plasma at which it begins to be excreted in the urine.
• t. traits — heritable traits which have specific thresholds, e.g. four rather than three toes on a guinea pig's hindfeet, alive or dead at a specific age.
• t. unit — the distance between two thresholds when an inherited abnormality can occur at a number of levels, e.g. completely patent ductus arteriosus, through partial closure (ductus diverticulum) and complete closure. See also threshold traits (above).

(thresh′ōld)
n

The lowest limit of stimulus capable of producing an impression on the consciousness or evoking a response in irritable tissue.

For a list of words related to threshold, see:

• Physiology - threshold: minimal level at which stimulus excites a response
• Building and Machine Parts - threshold: beveled strip, usu. wood or stone, fastened to doorsill directly below door

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See words rhyming with "threshold."

  See crossword solutions for the clue Threshold.

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Common misspelling(s) of threshold

• threshhold

Dansk (Danish)
n. - tærskel

Nederlands (Dutch)
drempel, grens

Français (French)
n. - (lit) seuil, (fig) seuil, (Fin, Impôt) seuil (d'imposition)

Deutsch (German)
n. - Schwelle

Ελληνική (Greek)
n. - κατώφλι, (απαρχ.) ουδός, (μτφ.) αφετηρία, ξεκίνημα, κατώτατο όριο

Italiano (Italian)
soglia

Português (Portuguese)
n. - começo (m), entrada (f), princípio (m), soleira (f)

Русский (Russian)
порог

Español (Spanish)
n. - umbral

Svenska (Swedish)
n. - tröskel

中文（简体）(Chinese (Simplified))
门槛, 开端, 入口

中文（繁體）(Chinese (Traditional))
n. - 門檻, 開端, 入口

한국어 (Korean)
n. - 문지방, 발단, 역

日本語 (Japanese)
n. - 敷居, 入口, 発端, 限界, 閾, 出発点
adj. - 敷居の, 限界をなす

العربيه (Arabic)
‏(الاسم) بدايه مستهل, عتبه‏

עברית (Hebrew)
n. - ‮סף, מפתן, גבול, קצה‬

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