Definitions

Diachronic: concerned with the way in which something, especially language, has developed through time. It is often contrasted with synchronic.

 Synchronic  concerned with something (especially a language) as it exists at one point in time. It is often contrasted with diachronic.

Standard: something used as a measure, norm, or model in comparative evaluations

The Neogrammarians were a German school of linguists, originally at the University of Leipzig, in the late 19th century who proposed the Neogrammarian hypothesis of the regularity of sound change

 Variable: not consistent or having a fixed pattern; liable to vary, able to be changed or adapted.

Discrete: individually separate and distinct.

Prescriptive: of or relating to the imposition of a rule or method.

Descriptive: describing or classifying without expressing judgment. Sources:Oxford University Press dictionary.