Ĭr'ri-ta-bĭl'i-ty, n.

n. [Fr. irritabilité, Sp. irritabilidad. It. irritabilità, Lat. irritabilitas.]

1. The quality of being easily irritated; susceptibility to excitement; the state of being irritable; vexation; exasperation; fretfulness; as, irritability of temper.
2. (Physiol.) (a.) A healthful vital susceptibility to the influence of natural, medicinal, and mechanical agents, and the power of responding in a normal manner, both by sensations and actions; especially, the property, in living tissue, of sudden contraction, followed by relaxation, produced by direct stimulus of its substance, or through the influence of the nerves. (b.) A morbid and plainly excessive vital susceptibility to the influence of natural, medicinal, and mechanical agents, and a capability of responding only by vitiated and abnormal sensations and actions. (c.) The general vital activity of any and every part of the living animal body, whether in health or disease;—so called upon the hypothesis that life is the result of organs in a state of stimulation.
3. (Bot.) The property, in plants, of exhibiting motion under the influence of certain stimuli.