ONlwSG

fèile f. [ˈfeːlə], gen. idem, ‘charm, incantation’. Zimmer (1895, 147) derives EG éle ‘prayer, chant, incantation’ from ON heill nt./f. ‘happiness; (good or bad) omen, sign; something that brings good luck, amulet’ (NO), 

So MacBain (1896), de Vries (1962), Schulze-Thulin (1996, 105) and McDonald (2009, 361). McDonald cites EG ‘éle, eib(h)il(l)’, inadvertently copying the latter form from his preceding entry (hefill). In discussion, Schrijver (1998, 141 + fn 6) writes heilla in error.

suggesting that either final ON -l has developed into [ə] in Early Gaelic or that the form borrowed was plural heilla, but the proposed parallel of CSc. -r > EG -a (e.g. CSc. iarlr > EG íarla ‘earl etc.’) is incorrect.

EG íarla derives from CSc. iarl acc., final -a [ə] being a Gaelic addition (s.v. iarla).

While ON ei would formally yield EG é, ON geminate ll – the second l here is part of the stem – would be expected to yield an unlenited, palatal [ʎ̪] /ʟ´/ <ll>´ in Early Gaelic rather than a lenited, palatal [l] /l´/ <l>´.

Stokes (1897, 62 line 12 fn 1, 72) dismisses Zimmer’s derivation, 

Acknowledged in MacBain 1911.

instead proposing that EG éle may be genuinely Celtic and cognate with W wylo ‘to weep’, i.e. from a verbal noun *ēg-lā (Schrijver 1998, 141 + fn 6). The suggestion in eDIL^˄ that EG éle is possibly taken from Matthew 27:46 

Eli, Eli, lama sabachthani? ‘my God, my God, why hast thou forsaken me? (King James Version; see also Psalm 22:1 and Mark 15:34).

is, as Schrijver says, most unlikely. EG éle yields SG fèile with prothetic f- regularly (MacBain 1896, 1911: †féile; 

MacBain’s (1892, 243–44) earlier translation ‘beneficence’ suggests he first considered the word was a normalised oblique form of fial ‘bounty, hospitality; liberality’ (Dwelly), cf. EG féle (< EG fíal ‘idem’).

so Dwelly 1911: †feile [sic] f.; MacLennan 1925: féile f.), cf. SG ailm > failm, q.v., and resorting to ON heill for a derivation appears unnecessary.

The word fèile ‘charm etc.’ is distinct from SG fèile ‘festival etc.’ (EG féil, féile < Lat. viglia (eDIL^˄)).