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asaileag f. [ˈas̪ilaɡ̊], also aisileag [ˈaʃilaɡ̊], gen. -leig -[læɡ̊ʲ], -[lɛɡ̊ʲ] ‘storm petrel, Hydrobates pelagicus’. This word is given as assilag (Martin 1698, 108; Buchan 1727, 21), ashilag (Macaulay 1764, 160), aslag mor 
?For aslag-mhara, with the lenited genitive of muir ‘sea’; mòr ‘large’ seems unlikely to be intended here.
Now Hydrobates pelagicus.
McDonald (2009, 339: likely; 2015a, 124–25: uncertain) derives aslag from ON áslákr, a poetic word for ‘cockerel’ and a form of the man’s name Ásleikr m., but the long stressed vowel in Old Norse militates against this. For aisileag, Henderson (1910, 123–24) suggests a connection with Scots asel ‘storm, cold sharp blast’ – as a harbinger of bad weather – (which Jakobsen (1928) relates to Norw. as in the sense ‘storm’ and the related verb ase), which on the face of it cannot be entirely ruled out, although the Old Norse antecedent is unknown. Mackenzie translates aisleag as ‘the little ferryman’, but this is a folk etymology based on SG aiseag m. ‘ferry’. Sommerfelt (1952a, 230 
So also McDonald (2009, 360).
One of the strategies for dealing with initial ON h- in Gaelic was to discard it, e.g. ON halsa ⇒ SG abhsadh, q.v., and loss of f before s in Gaelic reflexes of Old Norse loans does not appear to cause compensatory lengthening, e.g. ON *Sef-sætr > SG Seiseadar [ˈʃeˌʃad̪̥əɾ] (Cox 2022, 864–66 + fn 674), so that ON *haf-svala could be expected to yield EG *[ˈas̪əɫə] in the first instance, as Lockwood supposes, which might yield both SG *[ˈas̪əɫ̪ə] and *[ˈas̪ələ], 
With lenited broad /l/ yielding unlenited broad /ʟ/ and lenited slender /l’/, respectively.
With the variant spellings (f)amhlag and (f)aimhleag; cf. Ir. (Omeath) amhlóg ‘species of sea-gull’ (Dinneen 1947).
See also Coates 1988.