Old English butere "butter," general West Germanic (cf. 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, perhaps literally "cow-cheese," from bous "ox, cow" (see cow (n.)) + tyros "cheese;" 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. Butter-knife attested from 1818.