Irritation, n.
Etymology: [L. irritatio: cf. F. irritation.]
1. The act of irritating, or exciting, or the state of being irritated; excitement; stimulation, usually of an undue and uncomfortable kind; especially, excitement of anger or passion; provocation; annoyance; anger. The whole body of the arts and sciences composes one vast machinery for the irritation and development of the human intellect. De Quincey.
2. (Physiol.)
The act of exciting, or the condition of being excited to action, by stimulation; -- as, the condition of an organ of sense, when its nerve is affected by some external body; esp., the act of exciting muscle fibers to contraction, by artificial stimulation; as, the irritation of a motor nerve by electricity; also, the condition of a muscle and nerve, under such stimulation.
3. (Med.)
1 more senses
A condition of morbid excitability or oversensitiveness of an organ or part of the body; a state in which the application of ordinary stimuli produces pain or excessive or vitiated action.
Shades of meaning
Fernald has no entry of its own for irritation; he lists it under anger, pique.
Where he writes about it:
Impatience, fretfulness, irritation, peevishness, pettishness, petulance, and vexation express the slighter forms of anger. — from anger
Irritation, petulance, and vexation are temporary and for immediate cause. — from anger