The only free and comprehensive online etymological dictionary of the Spanish language
caballo (Noun) "horse"
10th cent. From Latin caballus 'id.' Of non-Indo-European origin. Borrowed from an unknown language in Asia with the root *kab- (compare Turkish käväl "swift (horse);" Russian kobýla "mare;" Old Church Slavonic koņь "horse"). Further consider Semitic words for camel with a structure *gam- (Akkadian gammalu, Hebrew gāmāl), hypothesized to be borrowed from an unattested word in Sumerian.
Also the origin of the surnames Caballero, Caballeros, first given to horsemongers.
Indo-European
Romance
Asturian caballu, Portuguese cavalo, Galician cabalo, Catalan cavall, French cheval, Italian cavallo, Aromanian cal, Romanian cal, Sardinian cadhu
Hellenic
Ancient Greek καβάλλιον (kabállion) "workhorse"