Re·ac·tion n.
 1. Any action in resisting other action or force; counter tendency; movement in a contrary direction; reverse action.
 2. Chem. 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.
 3. Med. 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.
 4. Mech. The force which a body subjected to the action of a force from another body exerts upon the latter body in the opposite direction.
    Reaction is always equal and opposite to action, that is to say, the actions of two bodies upon each other are always equal and in opposite directions.   --Sir I. Newton (3d Law of Motion).
 5. Politics Backward tendency or movement after revolution, reform, or great progress in any direction.
    The new king had, at the very moment at which his fame and fortune reached the highest point, predicted the coming reaction.   --Macaulay.
 6. Psycophysics A regular or characteristic response to a stimulation of the nerves.
 Reaction time Physiol., in nerve physiology, the interval between the application of a stimulus to an end organ of sense and the reaction or resulting movement; -- called also physiological time.
 Reaction wheel Mech., a water wheel driven by the reaction of water, usually one in which the water, entering it centrally, escapes at its periphery in a direction opposed to that of its motion by orifices at right angles, or inclined, to its radii.

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 Flame n.
 1. A stream of burning vapor or gas, emitting light and heat; darting or streaming fire; a blaze; a fire.
 2. Burning zeal or passion; elevated and noble enthusiasm; glowing imagination; passionate excitement or anger. “In a flame of zeal severe.”
    Where flames refin'd in breasts seraphic glow.   --Pope.
 Smit with the love of sister arts we came,
 And met congenial, mingling flame with flame.   --Pope.
 3. Ardor of affection; the passion of love.
 4. A person beloved; a sweetheart.
 Syn: -- Blaze; brightness; ardor. See Blaze.
 Flame bridge, a bridge wall. See Bridge, n., 5.
 Flame color, brilliant orange or yellow. --B. Jonson.
 Flame engine, an early name for the gas engine.
 Flame manometer, an instrument, invented by Koenig, to obtain graphic representation of the action of the human vocal organs. See Manometer.
 Flame reaction Chem., a method of testing for the presence of certain elements by the characteristic color imparted to a flame; as, sodium colors a flame yellow, potassium violet, lithium crimson, boracic acid green, etc.  Cf. Spectrum analysis, under Spectrum.
 Flame tree Bot., a tree with showy scarlet flowers, as the Rhododendron arboreum in India, and the Brachychiton acerifolium of Australia.