Noun
Any action in resisting other action or force; counter tendency; movement in a contrary direction; reverse action.
The mutual or reciprocal action of chemical agents upon each other, or the action upon such chemical agents of some form of energy, as heat, light, or electricity, resulting in a chemical change in one or more of these agents, with the production of new compounds or the manifestation of distinctive characters. See Blowpipe reaction, Flame reaction, under Blowpipe, and Flame.
An action induced by vital resistance to some other action; depression or exhaustion of vital force consequent on overexertion or overstimulation; heightened activity and overaction succeeding depression or shock.
The force which a body subjected to the action of a force from another body exerts upon the latter body in the opposite direction.
Backward tendency or movement after revolution, reform, or great progress in any direction.
Source: Webster's dictionaryTo every action there is always opposed an equal reaction. Isaac Newton
An abnormal reaction to an abnormal situation is normal behavior. Viktor Frankl
It is funny that men who are supposed to be scientific cannot get themselves to realise the basic principle of physics, that action and reaction are equal and opposite, that when you persecute people you always rouse them to be strong and stronger. Gertrude Stein
What a man calls his "conscience" is merely the mental action that follows a sentimental reaction after too much wine or love. Helen Rowland
Horror is the natural reaction to the last 5,000 years of history. Robert Anton Wilson
The world in general doesn't know what to make of originality; it is startled out of its comfortable habits of thought, and its first reaction is one of anger. W. Somerset Maugham