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-13c., descriven, "interpret, explain," a sense now obsolete; c. 1300, "represent orally or by writing," from Old French descrivre, descrire (13c.) and directly from Latin describere "to write down, copy; sketch, represent," from de "down" (see de-) + scribere "to write" (from PIE root *skribh- "to cut").
From late 14c. as "form or trace by motion;" c. 1400 as "delineate or mark the form or figure of, outline." Reconstructed with Latin spelling from c. 1450. Related: Described, describes, describing.
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Harper, D. (n.d.). Etymology of indescript. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/indescript