The term diachronic is essentially the concern about how something has changed or evolved over a specific amount of time. Most of the time this word is used when referring to the change in language used.

Modern linguistics encompasses both synchronic (studying language at a specific point in time) and diachronic (studying language change over time) approaches. While synchronic analysis focuses on the structure of language systems, diachronic analysis explores how languages evolve and change. Both perspectives contribute to our understanding of language.

Diachronic variation refers to changes in language over time. Some examples in English include shifts in pronunciation, such as the evolution of the "th" sound and changes in word meanings, like how the word "awful" used to mean "full of awe" but now means "bad." These variations occur naturally as languages evolve and adapt to new influences.

Bjarke Frellesvig has written:

'A case study in diachronic phonology' -- subject(s): Grammar, Historical, Historical Grammar, Japanese language, Phonology

according to the results of my conducted experiment ,the monochrinic has a shorter adaptation of level.the way i block the nostril has a direct effects on the efficiency of breathing.