(but′ər) noun
1. The fatty constituent of milk, separated by churning into a soft, whitish-yellow solid; also, this substance prepared and processed for cooking and table use.
2. A substance having the consistency or other qualities of butter, as the chlorides of some metals, a fruit preserve of a semisolid consistency: apple butter, and certain easily fused vegetable oils: peanut butter.
—to look as if butter would not melt in one's mouth To look innocent.
—v.t.
1. To put butter on.
2. Colloq. To flatter: usually with up.
—to know which side one's bread is buttered on To be aware of the true sources of one's fortune or security and to behave accordingly. [OE butere, ult. <Gk. boutyron <bous cow + tyros cheese]

(but′ər) noun
A person or animal that butts.