prescriptive adj.

late 14c., prescripcioun, in law, "a title or right acquired through long use or uninterrupted possession," from Old French prescription (13c.) and directly from Latin praescriptionem (nominative praescriptio) "a writing before, order, direction," noun of action from past participle stem of praescribere "write before, prefix in writing; ordain, determine in advance," from prae "before" (see pre-) + scribere "to write" (from PIE root *skribh- "to cut").

Meaning "act of establishing by rules" is from 1540s. The medical sense of "written directions from a doctor of the medicines or remedies to be used by a patient and the manner of using them" is recorded by 1570s. The word has been confused with proscription at least since c. 1400.

by 1963 in moral philosophy, "the view that moral judgments are prescriptions;" by 1977 in reference to language usage, "the belief that the grammar of a language should conform to its rules," hence often in hostile use, "belief that one variety of a language is superior to others and should be promoted, attempt to establish or maintain rules defining preferred or correct usage;" see prescriptive + -ism. Related: Prescriptivist.