fastness

n.

1. The condition or quality of being fast, especially:
   1. Firmness; security.
   2. Rapidity; swiftness.
2. The quality or condition of color retention; colorfastness.
3. 1. A secure or fortified place; a stronghold.
   2. A remote, secret place.

noun

Reliability in withstanding pressure, force, or stress: firmness, hardness, security, soundness, stability, stableness, steadiness, strength, sturdiness, sureness. See better/worse, change/persist, continue/stop/pause.

IN BRIEF: The quality of not being easily moved, freed or separated. Also: a fortified or secure place.

They depended upon the fastness of the fort for their safety.

Note: click on a word meaning below to see its connections and related words.

The noun has 3 meanings:

Meaning #1: a rate (usually rapid) at which something happens
  Synonyms: speed, swiftness

Meaning #2: the quality of being fixed in place
  Synonyms: fixedness, fixity, fixture, secureness

Meaning #3: a strongly fortified defensive structure
  Synonym: stronghold

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