Irritability

Noun

 * 1) The state or quality of being irritable; quick excitability; petulance; fretfulness; as, irritability of temper.
 * 2)  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.
 * 3)  A condition of morbid excitability of an organ or part of the body; undue susceptibility to the influence of stimuli.