Old English butere "butter, the fatty part of milk," obtained from cream by churning, general West Germanic (compare Old Frisian, Old High German butera, German Butter, Dutch boter), an early loan-word from Latin butyrum "butter" (source of Italian burro, Old French burre, French beurre), from Greek boutyron. This is apparently "cow-cheese," from bous "ox, cow" (from PIE root *gwou- "ox, bull, cow") + tyros "cheese" (from PIE root *teue- "to swell"); but this might be a folk etymology of a Scythian word.

The product was used from an early date in India, Iran and northern Europe, but not in ancient Greece and Rome. Herodotus described it (along with cannabis) among the oddities of the Scythians. In old chemistry, applied to certain substances of buttery consistency. Butter-knife, a small, dull knife used for cutting butter at the table, is attested from 1818.

Old English buterian "spread butter on," from the same source as butter (n.). The figurative meaning "to flatter lavishly" is by 1798 (with up (adv.), in Connelly's Spanish-English dictionary, p.413). Related: Buttered; buttering. To know which side one's bread is buttered on is to be able to take care of oneself.

"pertaining to basic material needs," from the noun phrase, "one's means of living," 1685, a figurative use of the words for the basic foodstuffs; see bread (n.) + butter (n.). Also, in reference to bread-and-butter as the typical food of young boys and girls, "of the age of growth; school-aged" (1620s).

variety of bean cultivated and eaten in the U.S., 1819, so called for its color, from butter (n.) + bean (n.).

liquid that remains after the butter has been churned out of milk, c. 1500, from butter (n.) + milk (n.). Compare German Buttermilch, Dutch botermelk. Middle French had laict beurré and babeurre.

Meaning "soured milk" by 1590s. Said to be either from a practice of letting the milk sour before churning to make the cream separate, or from the post-churning milk being more likely to sour with the cream removed. Modern buttermilk is made by adding bacteria cultures to pasteurized milk, which doesn't sour on its own.

also butter-nut, 1753, nut of the white walnut, a North American tree; transferred to the tree itself from 1783, from butter (n.) + nut (n.). So called from the oil it contains.

The dye made from the tree's inner bark was yellowish-brown, and the word was used (from 1861) to describe the Southern army troops in the American Civil War, but the exact reason is debatable. Many Southern uniforms seem to have been this color; perhaps butternut dye was extensively used in homemade uniforms (but the tree's natural range is mostly in the northeastern U.S.); perhaps some of the regulation gray uniforms faded or soiled to this color; perhaps it was because butternut was a nickname for Southerners in the Midwestern states.

"clumsy in the use of the hands, apt to let things fall," 1610s, from butter (n.) + finger (n.).

"pertaining to or derived from butter," 1823, from stem of Latin butyrum "butter" (see butter (n.)) + -ic.

"resembling butter," late 14c., from butter (n.) + -y (2). Related: Butteriness.

hydrocarbon radical, 1855, from butyric acid, a product of fermentation found in rancid butter, from Latin butyrum "butter" (see butter (n.)).