ONlwSG

eilean m. [ˈelan], gen. eilein -[æɲ], -[ɛɲ], ‘island’ goes back to EG ailén ‘idem’, hence Ir oileán and Mx ellen, all of which are derived by Zimmer (1888, 278–89) from ON eyland nt. ‘island’. MacBain (1986; 1911), Henderson (1910, 215) and Watson (1926, 91; 1929, 283) concur, while Craigie (1894, 162) considers the derivation not impossible. However, Oftedal (1956, 62 

Oftedal writes øyland in accordance with his usual practice, e.g. øy for ey f. ‘island’, øyrr for eyrr f. ‘gravel bank or sandbank’ (s.v. faoilinn) (Cox 2022, 49–50).

) notes that, while eilean is perhaps ultimately from Old Norse, the short stressed vowel in Gaelic is unexpected, 

Cox (1987 II, 64, s.v. Clach Eilistean) also suggests that SG eilean may be due to Old Norse influence, but does not elaborate.

and this is no doubt the basis of Marstrander’s (1915a, 120) rejection of the derivation: 

MacLennan (1925) notes Zimmer’s and Craigie’s support for and Marstrander’s rejection of a derivation from ON eyland. McDonald (2009, 352) misreads Marstrander as supporting one.

even though final ON -(l)and were to fall together with the Early Gaelic diminutive suffix -én (SG -an [an]) via morphemic substitution, the Old Norse diphthong ey would be expected to yield a long vowel in Gaelic (cf. CSc. ø̨yr acc. (later ON eyr) > SG aoir, s.v. faoilinn). EG ailén is most probably a diminutive form of EG ail ‘rock, boulder’, as assumed by eDIL^˄ and Vendryes (1996); for the vowel alternation a ~ o ~ e before a palatal consonant, cf. EG aile, later oile and eile ‘other’ (Ir. eile, SG eile, Mx elley), also the derivative forms EG ailech ‘rock, or rocky place’ ~ SG eileach and EG ailchiḋe ‘rocky, stony’ ~ SG eileachaidh (Watson 1926, 478).