irrespective (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., "relative, having relation or reference to something" (a sense now obsolete), from Medieval Latin respectivus "having regard for," from Latin respect- past-participle stem of respicere "look back at, regard, consider" (see respect (v.)). The meaning "relating or pertaining severally each to each, connected with each of those in question" is from 1640s.