means The process of carefully heating and cooling a material—like steel or chocolate—to give it the right hardness, strength, and texture.

from From Latin 'temperare,' meaning to mix in due proportion, moderate, or regulate—the same root that gives us 'temperature,' 'temper,' and 'temperate.' The thread tying them together is the idea of bringing something into balance: blending hot and cold, restraining excess, achieving the right mix. Metalworkers borrowed it for the heat-treating of blades, and the word kept its sense of disciplined moderation even as it spread to moods (a quick 'temper') and confectionery.