Asturian cabra, Portuguese cabra, Galician cabra, Catalan cabra, French chèvre, Italian capra, Aromanian caprã, Romanian capră, Sardinian craba
Gaulish gabrus, Old Irish caera "sheep" (from *kapera-), gabor, Middle Welsh gauar, Old Breton gabr, Old Cornish gauar
Old Norse hafr, Old English hæfer
Ancient Greek κάπρος (kápros) "boar"
Sanskrit kápṛth (?) "penis"
Note the variation between *ka- and *ga- in Celtic (cf. Old Irish caera "sheep" and gabor "roebuck"). Additionally, note the variation between *-b- in Celtic and *-p- in Greek and Latin. There is no way to explain the interchange between *ka- ~ *ga- and *-p- and *-b- from within Indo-European. The words must come from a non-Indo-European source or sources.