The Proto-Indo-European root *gʷou- "ox, bull, cow" became Proto-Germanic *kōuz, Old English cū, and English cow.
In Greek, *gʷou- became βοῦς bous "cow", which perhaps combined with τῡρός tūros "cheese" to form βού-τῡρον boutūron "butter". This was borrowed into Latin as būtȳrum. English butter is a very early, possibly pre-Old English borrowing of the Latin word.
τῡρός tūros is from the Proto-Indo-European *teuh₂- "to swell", which also gives us thousand from Proto-Germanic *þūs-hundi- "swollen hundred", and tumor from Latin tumēre "to swell".
And *teuh₂- gives us another dairy word: quark (the cheese), from Middle High German quarc from Old Church Slavonic тварогъ tvarogŭ.