ĭr'ri-tā'tion, n.

n. [Lat. irritatio, Fr. irritation, Sp. irritacion, It. irritazione.]

1Sense 1. The act of irritating or exciting; excitement, usually of an undue and uncomfortable kind; especially, excitement of anger or passion; provocation; exasperation; anger.

The whole body of the arts and sciences composes one vast machinery for the irritation and development of the human intellect. De Quincey.

2Sense 2. (Physiol.) (a.) A normal and appropriate action of an organized being under appropriate stimulus or conditions of action. (b.) A vitiated and abnormal sensation or action, or both in conjunction, produced by natural, medicinal, or mechanical agents. It is sometimes considered as an excess of vital action.

3Sense 3. (Med.) The act or process of stimulating muscular fiber; as, striated muscular fiber may be made to contract by irritation of its nerve.