Noah Webster
Irritation
IRRITA'TION, noun The operation of exciting heat, action, and redness in the skin or flesh of living animals, by friction or other means.
1. The excitement of action in the animal system by the application of food, medicines and the like.
2. Excitement of anger or passion; provocation; exasperation; anger.
3. In physiology, an exertion or change of some extreme part of the sensorium residing in the muscles or organs of sense, in consequence of the appulses of external bodies.
Irritation is the effect of a stimulus applied to an irritable part.