Proto-Indo-European Roots

Root/Stem: *gwu-
Meanings:  a bull, a cow
Cognates:
Hellenic Greek bous, boos (a bull)
Italic Latin bs, gen. bovis (a bull), Umbrian bum (acc. a bull), Volscian bim (gen. 'a bull'), Oscan Bvaiand (a place name)
Celtic Common Celtic *guhow-
Old Irish b, gen. bai (a bull), Welsh buw, Old Breton bou
Indic Sanskrit gaus (a bull)
Dardic & Nuristani
Iranian Avestan gus' (a bull), Persian gv (a cow)
Armenian Armenian kov 'a cow'
Tocharic Tocharic A ko, Tocharic B keu (a cow)
Thracian bonassos (a bull)
Germanic Common Germanic *kw- (a cow); > 
Old High German kuo (a cow), Old Saxon k (a cow), Old English c, Old Norse kr 
Swedish ko, German Kuh, Dutch koe
Baltic Common Baltic *guo-
Latvian guovs (a bull)
Slavic Common Slavic *gove,do (a cow, a bull) > 
Bulgarian & Serbian & Slovene govedo (a cow), Czech hovado, Slovak hovdo, Upper Sorbian howjado, Lower Sorbian gowedo (a cow), Old Russian gov'ado
Notes: A very ancient agricultural term, which could denote a cow when it was not domesticated yet. Nostratic cognates are also found for it: Semitic *g-w (a cow), Sumerian, Urartian & Hurritic gud, ngw (a bull) could be relatives.