means a feeling of mild annoyance or physical discomfort caused by something persistently bothersome.

from From Latin irritare, "to excite, provoke, or enrage," which gave us irritatio. The word slipped into English in the 1500s, first carrying the sense of stirring something up — whether a temper or a tender patch of skin. The root captures that same nagging energy: not a sudden blow, but a poking and prodding that won't quit.