irritation

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The act of irritating.
• noun The condition of being irritated; vexation.
• noun A source of irritation.
• noun An inflammatory reaction of a bodily part.
• noun Physiology The elicitation of a response to a stimulus in a plant or animal organ or tissue, especially in a nerve or muscle.

from The Century Dictionary.

• noun The act of irritating, or the state of being irritated; impatient or angry excitement; provocation; exasperation.
• noun Stimulation; incitement; a stirring up to activity.
• noun In physiology, the act of evoking some action, or change of state, in a muscle, nerve, or other living tissue, by some chemical, physical, or pathological agent; the state or action thus evoked.

from the GNU version of the Collaborative International Dictionary of English.

• noun 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.
• noun (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; ; also, the condition of a muscle and nerve, under such stimulation.
• noun (Med.) 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.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun 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.
• noun 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.
• noun 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.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a sudden outburst of anger
• noun the neural or electrical arousal of an organ or muscle or gland
• noun the psychological state of being irritated or annoyed
• noun the act of troubling or annoying someone
• noun an uncomfortable feeling of mental painfulness or distress
• noun unfriendly behavior that causes anger or resentment
• noun (pathology) abnormal sensitivity to stimulation