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"easily irritated," 1592, teachie, in "Romeo & Juliet" I.iii.32; of uncertain origin. Perhaps from Middle English tatch "a mark, quality," derived via Old French from Vulgar Latin *tecca, from a Germanic source akin to Old English tacen (see token).
Irritable; irascible; testy: the days when tetchy film crews invaded the center of soporific conferences
[1592+; fr dialect tetched, ''crazy, touched in the head'']