irreverence (n.)

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.

"regard with deep respect and veneration," 1660s, from French révérer, from Latin revereri "revere, fear," from re-, here perhaps an intensive prefix (see re-), + vereri "stand in awe of, fear, respect" (from PIE root *wer- (3) "perceive, watch out for"). Reverence was the earlier form of the verb. Related: Revered; revering.