Publishing history:v1.0
v1.0: 05/06/26
alc f. [ɑɫ̪̥k], gen. ailc(e) [ˈal̥kʲ(ə)], ‘razorbill, lesser auk, Alca torda’ (also ‘guillemot’ (CG II, 223: ‘[t]he razorbill and the guillemot resemble one another closely, and at some distance can only be distinguished by the practised eye’)); alc [ɑɫk] 
For the (read voiceless) non-dental velarised lateral, see Cox 2022, 14.
Also in Lochs (Christiansen 1938, 4, 16).
Via back-formation, where morphophonemically the initial vowel has been reinterpreted as the lenited reflex of /fV/-, e.g. (after the radical feminine article) an alc [ə ˈᵰ̪ɑɫ̪̥k] > an fhalc [idem] > (unlenited) falc; cf. Coates 1988: ‘... the present Hebridean form being an unhistorical nominative inferred from /alk/ [leg. /ɑʟk/] (as if this were a form representable orthographically as fhalg [leg. fhalc])’.
McDonald (2009, 339; 2015, 122) gives ON álka, alc; Mackay (1897, 93) Ice. alk.