Two etymologies of (P)IE lambs have external comparanda:
Gloss: ‘lamb’ (item 36 in Bjørn 2017)
Attestations: Goth. lamb ‘sheep’; (?)Gr. ἒλαφος ‘red deer’
Notes: If rightly connected by Kroonen, this root has very limited and semantically difficult IE distribution, and for both branches necessarily different Ablaut grades (2013: 325f.). The traditional etymology for the Greek item departs from a possible Aeolic origin of the alternate form ἐλλός ‘fawn’ < *el-n-os, cf. Arm. eln ‘id.’, Lith. élnis ‘id.’, OCS elenĭ ‘id.’, Welsh elain ‘id.’ (e.g. Frisk 1960: 483ff.). Adams surely connects to these forms Toch. A yäl ‘gazelle’, B yal ‘id.’ and the rather elusive Hit. aliyan(a)- ‘(?)roebuck’ (2013:523 [note: contra Mallory & Adams, who connect it to Hit. ali- ‘soft’ (1997: 154)]), and further, more semantically tantalizing, Toch. B āl– ‘ram’ (2013:58). The labial obstruent in the main Greek lemma has then been compared to the identical ending of ἒρι-φος ‘youngling’ that is decisively derivational in Ved. vṛṣa-bhá– ‘bull’ from vr ́ṣan– ‘manly, powerful’ (Chantraine 1968: 333,372). This PIE suffix *-bhé– may be relevant for Germanic regardless of the heritage. Lehmann hesitantly connects all of the above from a root *el- ‘brown’ (1986: 226), which may as well be fitted with the initial laryngeal *h1-, but Germanic is formally difficult to include in this bulk. The Greek branch, along with its possible cognates, would surely help establish the root as of PIE origin, but the comparison is doubtful. [NOTE: See now also Vrieland 2017 in favor of the wider connection]
NE Caucasian: *ɫVmbagV ‘sheep’ > Avar lémag, Akhvakh lãgi; Lezghian lap:ag
Discussion: What appears to be a new comparison nonetheless suggests itself straightforwardly with almost perfect alignment of three identical radicals; moreover, the Avar gloss is a) ‘sheep’ b) ‘1yr old sheep’ (NCED s.v.), mirroring the Germanic semantics. According to Nikolayev & Starostin the NE Caucasian form is likely to have been borrowed (ibid.). It is possible that this lexeme at an early stage complimented the proper PIE *h3ewi- ‘sheep’ (item 58), either as a loan from an unidentified source but in common with NE Caucasian, or as an internal derivation; the semantic fate in Germanic and possible elsewhere in IE surely indicates a kind of specialization. The lexeme was transferred into Finnish lammas ‘sheep’ from a Germanic language spoken in the Baltic region, either Gutnish or Gothic (Kroonen 2013: 326), both of which developed (or retained) the less specialized meaning. The connection may thus be compared to PIE *h2e(i)ĝ- ‘goat’ (item 40) as a lexical isogloss unique to NE Caucasian and western IE.
Gloss: ‘lamb’ (item 45 in Bjørn 2017)
Attestations: Lat. agnus; OIr. úan; OEng. ēanian ‘to yean’; OCS agnę; Gr. ἀμνός
Notes: Attestations reflect limited distribution, that nonetheless seems tightknit despite minor differences (Frisk 1969: 93f.). The item cannot be posited for the earlier stages of PIE, and appear to be a European regionalism.
Semitic: *igl– ‘young animal’ (Gamkrelidze & Ivanov 1995: 769 [Add.: also Blažek 1996])
Discussion: Orel & Stolbova connect Semitic with cognates in Central Chadic, Cushitic, and Omotic to establish Afro-Asiatic *igal ‘cow, calf’ (1995: 247), and note should be made of the semantics that are consistently bovine except for the generalization that incurred very sporadically in Ge’ez to ‘young animal’ and possibly also Akkadian agalu ‘donkey’. Gamkrelidze & Ivanov choose to weigh the more general meaning (ibid.) that more readily resonates with the (P)IE reconstruction despite considerable evidence pointing to the conclusion of higher specialization (cf. also Diakonoff 1985: 129f.); the Semitic comparanda should consequently be rejected. Rather, the word may be connected with *h2e(i)ĝ- ‘goat’ (item 40), which requires both semantic drift and an explanation of the formally incompatible velars, that may be ascribed to its putative foreign nature.