bread-and-butter adj.

"kind of food made from flour or the meal of some grain, kneaded into a dough, fermented, and baked," Old English bread "bit, crumb, morsel; bread," cognate with Old Norse brauð, Danish brød, Old Frisian brad, Middle Dutch brot, Dutch brood, German Brot.

According to one theory [Watkins, etc.] from Proto-Germanic *brautham, from PIE root *bhreu- "to boil, bubble, effervesce, burn," in reference to the leavening. But OED argues at some length for the basic sense being not "cooked food" but "piece of food," and the Old English word deriving from a Proto-Germanic *braudsmon- "fragments, bits" (cognate with Old High German brosma "crumb," Old English breotan "to break in pieces") and being related to the root of break (v.). It cites Slovenian kruh "bread," literally "a piece."

Either way, by c. 1200 it had replaced the usual Old English word for "bread," which was hlaf (see loaf (n.)).

The extended sense of "food, sustenance in general" (late 12c.) is perhaps via the Lord's Prayer. The slang meaning "money" dates from 1940s, but compare breadwinner, and bread as "one's livelihood" dates to 1719. Bread and circuses (1914) is from Latin, in reference to food and entertainment provided by the government to keep the populace content. "Duas tantum res anxius optat, Panem et circenses" [Juvenal, Sat. x.80].

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.