1. Capable of reacting to a stimulus. 2. Tending to react immoderately to a stimulus. Cf.:excitable.
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a) easily exasperated or excited
b) responsive to stimuli
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ir·ri·ta·ble (irґĭ-tə-bəl) [L. irritare to tease] 1. capable of reacting to a stimulus. 2. abnormally sensitive to a stimulus. 3. prone to excessive anger, annoyance, or impatience.Medical dictionary. 2011.