1. Gen. sing.—-οιο, the original form, appears in Hom. πολέμοιο. By loss of ι ( cross43) comes -οο, which is sometimes read in Hom. (Αἰόλοο for Αἰόλου κ cross36). By contraction of οο comes -ου found in Hom., Ionic, Milder Doric. οο yields ω in Aeolic and Severer Doric (ἵππω).
2. Dual.—-οιιν in Hom. (ἵπποιιν).
3. Dat. pl.—-οισι (ν) Hom., Aeolic, Ionic.
4. Acc. pl.—-ους is from -ον-ς (found in Cretan), that is, the accus. sing. + ς. From -ονς comes -ως Severer Doric, -οις Aeolic, -ος Cretan and in Dor. poetry. -ους is Hom., Ionic, and Milder Doric.
Herbert Weir Smyth [n.d.], A Greek Grammar for Colleges; Machine readable text [info] [word count] [Smyth].