But its lack of a Proto-Indo-European thematic vowel (o or e) and of any nominative singular ending (ordinarily -s or -os) doesn't neatly place it within either of the Proto-Indo-European nominal categories, thematic and athematic.
Its lack of a thematic Proto-Indo-European vowel (o or e) and an ordinary nominative singular ending (usually -s or -os) means it doesn't easily fit into the thematic or athematic categories of Proto-Indo-European nominals.