Irritation

n.	1.
	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.) 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.

Noun	1.	irritation - the psychological state of being irritated or annoyed Synonyms: annoyance, botheration, vexation
	2.	irritation - a sudden outburst of anger; "his temper sparked like damp firewood" Synonyms: temper, pique
	3.	irritation - (pathology) abnormal sensitivity to stimulation; "any food produced irritation of the stomach"
	4.	irritation - the neural or electrical arousal of an organ or muscle or gland Synonyms: innervation, excitation
	5.	irritation - an uncomfortable feeling in some part of the body Synonyms: discomfort, soreness
	6.	irritation - unfriendly behavior that causes anger or resentment Synonyms: provocation, aggravation
	7.	irritation - the act of troubling or annoying someone Synonyms: annoying, vexation, annoyance

adverse circumstances, adversity, affliction, aggravation, agitation, algesia, amplification, animation, arousal, arousing, augmentation, blight, bummer, care, chafe, contentiousness, cross, curse, deepening, deliberate aggravation, deterioration, difficulties, difficulty, disapprobation, disapproval, discontent, displeasure, dissatisfaction, downer, electrification, embittering, embitterment, enhancement, enlargement, exacerbation, excitation, excitement, exhilaration, festering, firing, fomentation, fret, gall, galvanization, hard knocks, hard life, hard lot, hardcase, hardship, heightening, incitation, incitement, increase, inflammation, infuriation, instigation, intensification, irritant, lathering up, magnification, pep rally, pep talk, perturbation, plight, predicament, pressure, provocation, rabble-rousing, rankling, resentfulness, resentment, rigor, sea of troubles, sensitiveness, sharpening, sore, sore spot, soreness, souring, steaming up, stimulation, stimulus, stirring, stirring up, stirring-up, stress, stress of life, tenderness, trial, tribulation, trouble, troubles, vale of tears, vicissitude, whipping up, working up, worsening