Meaning

verb cause annoyance in; disturb, especially by minor irritations

verb excite to an abnormal condition, or chafe or inflame

verb excite to some characteristic action or condition, such as motion, contraction, or nervous impulse, by the application of a stimulus

originBorrowed from Latin irritātus, perfect passive participle of irritō (“to invalidate, render void, annul”) (see -ate (verb-forming suffix)), from irritus (“invalid”), the equivalent of in- + ratus (“valid, established, fixed”).

Etymology from Wiktionary, CC BY-SA 3.0