Noun
o-grade (uncountable)
(Indo-European studies) In Proto-Indo-European linguistics, an ablaut form of a Proto-Indo-European root, characterised by the presence of the */o/ vowel phoneme in place of */e/.
Ancient Greek γόνος (gónos) is a reflex of *ǵónh₁os (“race”), which is itself an o-grade derivative of the root *ǵenh₁- (“to beget; to produce, bear”).
Coordinate terms: e-grade, zero-grade