To make trim. The Italians say, temperare la lira, to tune the lyre: temperare una penna, to mend a pen; temperáre l'oriuôlo, to wind up the clock. In Latin, temperare calamum is “to mend a pen.” Metal well tempered is metal made trim or meet for its use, and if not so it is called ill-tempered. When Otway says, “Woman, nature made thee to temper man,” he means to make him trim, to soften his nature, to mend him.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894