(n.) The state or quality of being irritable; quick
excitability; petulance; fretfulness; as, irritability of temper.
(n.) 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; esp., the property which living muscle processes, of
responding either to a direct stimulus of its substance, or to the
stimulating influence of its nerve fibers, the response being indicated
by a change of form, or contraction; contractility.
(n.) A condition of morbid excitability of an organ or
part of the body; undue susceptibility to the influence of stimuli. See
Irritation, n., 3.
