temper (v.)

"mix or work up into proper condition, adjust or restore to proper proportions;" Middle English temperen, from late Old English temprian "to moderate by mixture, bring to a proper or suitable state, modify (some excessive quality), restrain within due limits," from Latin temperare "observe proper measure, be moderate, restrain oneself," also transitive, "mix correctly, mix in due proportion; regulate, rule, govern, manage."

This often is described as from Latin tempus "time, season" (see temporal (adj.1)), with a notion of "proper time or season." But as the root sense of tempus seems to be "stretch," the words in the "restrain, modify" sense might be from a semantic shift from "stretching" to "measuring" (compare temple (n.1)).

The meaning "make (steel) hard and elastic" is from late 14c. The sense of "tune the pitch of a musical instrument" is recorded from c. 1300. Related: Tempered; tempering.

late 14c., "due proportion of elements or qualities," in reference to bodily humors, medicinal ingredients, etc., from temper (v.). Also "moderation, restraint," also "temperance" (early 15c.); "calm state of mind, tranquility" (c. 1600).

The sense of "characteristic state of mind, inclination, disposition" is attested by 1590s, based on the supposed effect of the humors in old physiology (compare temperament). The meaning "angry state of mind, disposition to give way to anger" (for bad temper) is by 1828. The meaning "degree of hardness and resiliency in steel" is attested from mid-15c.