Variant Forms of the Genitive
In Early Modern Irish, there is some latitude in the formation of the genitive for certain nouns. [Desiderius, p. xxiii-xxiv]
Examples:
Nominative Genitive
blas blais or blasa
aoibhneas aoibhnis or aoibhneasa
grádh grádha or gráidh
duine daoine or daoineadh