Two words with very plausible external relations denote the bovine species:
Gloss: ‘cow’ (item 30 in Bjørn 2017)
HLuw. wa/i-wa/i-(i); Toch. A ko, Toch. B keu; Umb. bum (acc.); OIr. bō; ON kýr; Latv. gùovs; OCS go-mĭno ‘threshing floor’; Alb. ka; Myc. qo-u-, Gr. βοῦς; Arm. kov; Ved. gáu-, Av. gāuš.
Albanian shows some irregularity in the exact type of velar (Mallory & Adams 1997: 134ff.), but does not question the PIE reconstruction. The phonetic complements in Hittite (GUD-us, GUD-un) do allow a continuation of this root, but cannot be known for certain (Gamkrelidze & Ivanov 1995: 483), but the Hieroglyphic Luwian attestation appears solidify evidence for the Anatolian branch (Melchert 2003: 195).
Semitic: *ġi ‘to bellow’ (Schott 1936: 66f.)
Egyptian: gw ‘bull’ (Mallory & Adams 1997: 135)
Kartvelian: *pur (attestations see Klimov 1998: 206)
NW Caucasian: *č’:amə > e.g. Kabardian gwaw ‘bull’ (Nichols 1997: 143)
NE Caucasian: *ʒ ̣̌VW > e.g. Chechen-Ingush govr ‘horse’ (ibid.)
Sumerian: gu4 ~ gud ‘bull’
It is likely that the PIE root originally was generic only for the species (and not also for the gender), denoting both ‘cow’ and ‘bull’, i.e. ‘cattle’ (cf. Gamkrelidze & Ivanov 1995: 482), which is practically demanded by the external comparanda. According to Mallory & Adams the domestication of the cow began during the Neolithic revolution in the Middle East in the 7th millennium BC and had spread through Europe by the inception of the fourth (1997: 137). Considering the rather extensive list of proposed comparanda, the possibility of onomatopoetic homophony may justifiably be argued, but the ostensible motivation is elusive and perhaps best represented by the Semitic verbal connection proposed by Schott, but it is weak compared to all other comparanda that clearly relate a very narrow semantic value to each other; the only possible scenario that could comprise this root as viable would be as the primordial verbal root from which the term was originally derived. Against this notion, the Egyptian evidence stands comparatively stronger denoting the animal itself and seems strengthened by further Afro-Asiatic cognates in West Chadic *warar ‘vicious bull’ (Orel & Stolbova 1995: 527). These forms may gain further credibility through the similarly positive situation in Sumerian (cf. Sahala 2009: 7) that represents the earliest attestation and is perpetuated as Sumerograms in Hittite where it curiously eclipses a word that might ultimately be related. Further suggested borrowings include Old Chinese (Mallory & Adams 1997: 135), but especially noteworthy is the proposed connection to Altaic which includes a demonstrable semantic generalization that allows a shift to other quadrupeds, cf. as a link
Manchurian geo ‘mare; cow; female (of quadrupeds)’ and consequently Classical Mongol gegün ‘mare’ (Gamkrelidze & Ivanov 1995: 491f.), particularly relevant for the inclusion of the NE Caucasian comparandum suggested by Nichols (1997: 143). The NW Caucasian attestation, obviously semantically incompatible with its western neighbors, is formally interesting from a PIE point of view as it retains an initial labiovelar. Labiality is also the proposed recipient rendition of *gw– in Kartvelian [ADD: Nichols doesn’t consider the forms related, but for the sake of argument I’ll leave it here as my own suggestion], which necessitates either an early borrowing directly from PIE, a centum continuant, or a non-IE language with similar retention of the feature, e.g. NW Caucasian, but the proposed concordance poorly matches ‘to extinguish’ (item 110) where PIE *gw– yields Kartvelian *kw-, and is therefore quite improbable. All things considered the item may well be foreign in PIE, but it is of considerable age; it seems to significantly predate the spread of other agricultural terms, e.g. *(s)teuros ‘bull’ (item 118), but may, too, be connected with the same general wave of technological innovation, as widespread borrowings certainly suggest. The somewhat difficult Anatolian material could be secondarily introduced, but there is no imperative to favor such an interpretation.
Gloss: ‘bull’ (item 118 in Bjørn 2017)
PIE (1) *steuros
Attestations: OHG stior; Av. staora– ‘large (domestic) animal (i.e. horse, ass, cow, camel)’
Notes: The suggested Avestan correlate to OHG stior may also derive from *steh2uro– ‘big’ (Kroonen 2013: 478), which would render the Germanic forms isolated.
PIE (2) *tauros
Attestations: (?)Lat. taurus; Gaul. tarvos; ON þjórr; OPrus. tauris ‘bison’; OCS turŭ ‘aurochs, bull’; Alb. ter; Gr. ταῦρος; Khot. ttura– ‘mountain goat’
Notes: Celtic shows metathesis, but fits otherwise unproblematically with the European cognates. Germanic has *-e- instead of *-a-, which has been explained as analogy to *steur-, but see the discussion immediately below for a different solution. [Add. Latin is expected to show metathesis of the sequence *auRV > aRvV, suggesting that it might be a relatelively late borrowing (Weiss 2009: 157).] The Khotanese item, however, stands out semantically, but fits with the Avestan continuation of PIE (1) *steur- if part of a Proto-Iranian shift as suggested by Bailey (1979: 132).
Semitic: *tawr > Akk. šūru, Arab. tawr, Heb. šôr, etc. (Bomhard 1981: 416)
Semitic (alt.): Arab. ṭaraḳa ‘to impregnate (of camels)’ (Schott 1936: 78)
NE Caucasian: *stw– (Nichols 1997: 143)
Discussion: The very obvious correlation between the Semitic and IE forms certainly suggests them as related, obvious even to philologists (Levin 1995, cf. § 3.2.6). The nature of this relation, however, is disputed. Schott’s attempt at a connection with Arabic ṭaraḳa ‘to impregnate (of camels)’ to substantiate internal semitic derivation (1936: 78) is improbable, potentially even more so in light of Militarev & Kogan’s Afro-Asiatic reconstruction (2005:307ff.) that nonetheless requires some semantic leniency, covering both ‘elephant’ (Central Chadic) and ‘rhinoceros’ (Northern Omotic), but it is noteworthy that Orel & Stolbova do not include to form (1995), and Lipińsky seems to share this uncertainty of origin (1997: 561) [Add. This could shed new light on the Avestan comparandum, although it becomes chronologically strained.]. The two disparate PIE words, although clearly related, seem to have entered the language at two different stages; *steuros likely prior to *tauros, where the latter is phonetically less complex and also brands a-vocalism. Dolgopolsky initially considered the IE complex descendants of a single form borrowed directly from proto-Semitic into PIE (1987: 14), but later suggested only partial common heritage for Semitic and PIE that was subsequently confounded by a loan (1993: 244). Weak Indo-Iranian evidence, however, as well as a complete lack of Anatolian and Tocharian cognates, question the antiquity of the noun in PIE while the Semitic provenance itself may be inhibited by the questionable nature of the Afro-Asiatic evidence for the root. Alternatively, Kroonen suggests that the e-vocalism in Germanic *steur- and *teur– is a consequence of raising from an otherwise unidentified donor language (cf. Haarmann 1994: 269f. and the treatment of *ghaid-, item 21) that similarly shows up in Etruscan thevru– (2013: 540), and may additionally account for the Germanic forms with initial s- from a foreign spirant not found at the recipient stage of the language (2013: 478). Nichols’s suggestion of a NE Caucasian*stw– (1997: 143) is tantalizing as it seemingly reflects the sporadic s-forms in IE, but the root is not included by Nikolayev & Starostin (NCED) and has not been validated.