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Irritability

1. The state or quality of being irritable; quick excitability; petulance; fretfulness; as, irritability of temper.

2. (Science: physiology) a natural susceptibility, characteristic of all living organisms, tissues, and cells, to the influence of certain stimuli, response being manifested in a variety of ways, as that quality in plants by which they exhibit motion under suitable stimulation; especially, the property which living muscle processes, of responding either to a direct stimulus of its substance, or to the stimulating influence of its nerve fibres, the response being indicated by a change of form, or contraction; contractility.

3. (Science: medicine) a condition of morbid excitability of an organ or part of the body; undue susceptibility to the influence of stimuli. See irritation.

Origin: L. Irritabilitas: cf. F. Irritabilite.