attemper (v.)

late 14c., "reduce, moderate, modify; restrain, control; make fit or suitable; mix in just proportion," from Old French atemprer "become moderate, regulate one's actions, take the middle way," from Latin attemperare, from assimilated form of ad "to" (see ad-) + temperare "to mix in due proportion, modify, blend; restrain oneself" (see temper (v.)). Related: Attempered; attempering.