Origin and history of intemperate

"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.

word-forming element meaning "not, opposite of, without" (also im-, il-, ir- by assimilation of -n- with following consonant, a tendency which began in later Latin), from Latin in- "not," cognate with Greek an-, Old English un-, all from PIE root *ne- "not."

In Old French and Middle English often en-, but most of these forms have not survived in Modern English, and the few that do (enemy, for instance) no longer are felt as negative. The rule of thumb in English has been to use in- with obviously Latin elements, un- with native or nativized ones.