buttermilk n.

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.

"opaque white fluid secreted by mammary glands of female mammals, suited to the nourishment of their young," Middle English milk, from Old English meoluc (West Saxon), milc (Anglian), from Proto-Germanic *meluk- "milk" (source also of Old Norse mjolk, Old Frisian melok, Old Saxon miluk, Dutch melk, Old High German miluh, German Milch, Gothic miluks), from *melk- "to milk," from PIE root *melg- "to wipe, to rub off," also "to stroke; to milk," in reference to the hand motion involved in milking an animal. Old Church Slavonic noun meleko (Russian moloko, Czech mleko) is considered to be adopted from Germanic.

Of milk-like plant juices or saps from c. 1200. Milk chocolate (eating chocolate made with milk solids, paler and sweeter) is recorded by 1723; milk shake was used from 1889 for a variety of concoctions, but the modern version (composed of milk, flavoring, etc., mixed by shaking) is from the 1930s. Milk tooth (1727) uses the word in its figurative sense "period of infancy," attested from 17c. To cry over spilt milk (representing anything which, once misused, cannot be recovered) is first attested 1836 in writing of Canadian humorist Thomas C. Haliburton. Milk and honey is from the Old Testament phrase describing the richness of the Promised Land (Numbers xvi.13, Old English meolc and hunie). Milk of human kindness is from "Macbeth" (1605).