It is not clear what name underlies the spelling Aisil, which occurs nowhere else outside DB. Von Feilitzen was rightly cautious in suggesting that ‘If native perhaps from OE Æðelsige . . . with inorganic –l’ (von Feilitzen 1937: 142), since the DB forms for Æthelsige have hardly ever lost the first –l–, and the addition of an unnecessary (‘inorganic’) final –l is also a rarity. It may be more plausible to suggest that the letters of the name had been transposed, turning Ailsi (for Æthelsige) into Aisil. Any other suggestion would require multiple errors in the transcription of the name into GDB.
The DB entry including Aisil was entered in duplicate, probably by copying twice from the same exemplar (rather than internal copying from the manuscript of GDB itself, since it would have been awkward to copy from a recto at the end of a quire to a verso earlier in the same quire). That suggests that the name read Aisil in the exemplar and was accurately copied twice over, but it does not help to elucidate the origin of the name.
Both Phillimore and Alecto render the name Aisil.
von Feilitzen 1937: O. von Feilitzen, The Pre-Conquest Personal Names of Domesday Book, Nomina Germanica 3 (Uppsala, 1937)
Spellings in Domesday Book: Aisil
Forms in modern scholarship:
von Feilitzen head forms: Aisil
Phillimore edition: Aisil
Alecto edition: Aisil