(1):

(a.) Endowed with irritability; susceptible of irritation; capable of being excited to action by the application of certain stimuli.

(2):

(a.) Susceptible of irritation; unduly sensitive to irritants or stimuli. See Irritation, n., 3.

(3):

(a.) Capable of being irriated.

(4):

(a.) Very susceptible of anger or passion; easily inflamed or exasperated; as, an irritable temper.