What is temper? What is temper? To modify by the addition of a moderating element; moderate: "temper its doctrinaire logic with a little practical wisdom” ( Robert H. Jackson). See Synonyms at moderate.To bring to a desired consistency, texture, hardness, or other physical condition by or as if by blending, admixing, or kneading: temper clay; paints that had been tempered with oil. To harden or strengthen (metal or glass) by application of heat or by heating and cooling. To strengthen through experience or hardship; toughen: soldiers who had been tempered by combat. To adjust finely; attune: a portfolio that is tempered to the investor's needs. Music To adjust (the pitch of an instrument) to a temperament.To be or become tempered.A state of mind or emotions; disposition: an even temper. See Synonyms at mood1.Calmness of mind or emotions; composure: lose one's temper. A tendency to become easily angry or irritable: a quick temper. An outburst of rage: a fit of temper. A characteristic general quality; tone: heroes who exemplified the medieval temper; the politicized temper of the 1930s. The condition of being tempered.The degree of hardness and elasticity of a metal, chiefly steel, achieved by tempering.A modifying substance or agent added to something else.Archaic A middle course between extremes; a mean.