irrespective (adj.)

1620s (implied in irrespectively), "disrespectful," from assimilated form of in- (1) "not, opposite of" + respective in its sense of "regardful." Meaning "without taking account of particular circumstances or conditions" had developed by 1690s, from the notion of "not observing or noting with attention." In modern use it tends to be adverbial, in irrespective of, a use attested by c. 1800.