insufficient 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.

early 14c., from Old French soficient "satisfactory," or directly from Latin sufficientem (nominative sufficiens) "adequate," present participle of sufficere "to supply as a substitute," from sub "up to" (see sub-) + combining form of facere "to make, to do" (from PIE root *dhe- "to set, put").

1520s, from Old French insufficience and directly from Late Latin insufficientia "insufficience," abstract noun from insufficientem "insufficient" (see insufficient). Insufficience "deficiency" is from early 15c.