imprescriptible adj.

word-forming element meaning "not, opposite of, without" (also im-, il-, ir- by assimilation of -n- with following consonant, a tendency which began in later Latin), from Latin in- "not," cognate with Greek an-, Old English un-, all from PIE root *ne- "not."

In Old French and Middle English often en-, but most of these forms have not survived in Modern English, and the few that do (enemy, for instance) no longer are felt as negative. The rule of thumb in English has been to use in- with obviously Latin elements, un- with native or nativized ones.

mid-15c., prescriben, "to write down as a direction, law, or rule," from Latin praescribere "write before, prefix in writing; ordain, determine in advance," from prae "before" (see pre-) + scribere "to write" (from PIE root *skribh- "to cut"). Related: Prescribed; prescribing. Medical sense of "advise, appoint, or designate as a remedy for a disease" is from 1580s, probably a back formation from prescription.