Etymology: A Common Germanic and Common Indo-germanic word: Old English cú = Old Frisian kú, Old Saxon có (Middle Dutch koe, Dutch koe, Low German ko), Old High German chuo (Middle High German kuo, German kuh), Icelandic kýr accusative and dative kú ( < kû-z, Swedish, Danish ko, koe) < Old Germanic *kōu-z, *kô-z, feminine < Aryan g^wōus, accusative g^wōm, whence Sanskrit gāús, gām, gav-, go-, Greek βοῦς, βοϝ-, βο-, Latin bōs, bov-, bo-, ox; the word being of both genders outside Germanic. The ū in Old English, Frisian, and Old Norse, against the original ō retained in Old Saxon and Old High German, is perhaps to be explained from an original Germanic inflection kō(u)s , kôm , kôwez , kôwi , plural kôwez , kôwôm , kō(u)miz , whence, by regular passage of original ôw before vowels into û , genitive kûiz , dative kûi , plural kûiz , etc. Hence by levelling in the separate languages, kô- or kû- (umlaut kŷ- ), throughout. (Prof. Sievers.) The Old English inflection was: Singular genitive cúe , cú , later, after o- stems, cuus , cús ; dative cý ; Plural nominative accusative cýe , cý , genitive cúa , later, after n- stems, cúna , northern cýna ; dative cúum . The umlaut plural cýe , cý , < Old Germanic *kôwez , kûiz (compare also Old Norse kýr , Old Saxon koji , Old High German chuowi , chuoi (chuoji ), chuo , German kühe ) gave regularly Middle English ky , kye , still retained in Scots and Northern English. But Southern English at an early period took an extended form kȳn , later kyne , kine , still used, with slightly archaic flavour, beside the later cows , which hardly appears before the 17th cent. Middle English kȳn is to be compared with brethren , children , and other southern plurals in -n . In this particular case, the use of the genitive plural cúna , cýna (in 12th cent. cune , kyne ) with numerals (see 1b β), may have contributed to the prevalence of the kȳn, kyne form.