Irritated, impatient, or exasperated; peevish: a testy cab driver; a testy refusal to help.
Origin: Alteration of Middle English testif, headstrong, from Old French testu, from teste, head, from Late Latin testa, skull; see teston.
Word History: To the casual eye testy and heady seem to have no connection; a more thoughtful examination reveals that both words refer to the head. The head in heady is easy to see in both the form and meanings of the word. The earliest sense, first recorded in a work composed before 1382, is “headlong, headstrong,” which is clearly a “head” sense; but so is the better-known current sense “apt to go to the head, intoxicating.” To see the head in testy, we must look back to the Old French word testu, the source of our word. Testu is derived from the Old French word teste, “head” (Modern French tête). In English testy developed another sense, “aggressive, contentious,” which passed into the sense we are familiar with, “irritable.”