4.2.4. In Diphthong

1. There are long diphthongs -au, -eu, -ou, -ei, which sometimes present short vowels, as well as other endings without diphthong, i.e., -a, -e, -o.

NOTE. The last are probably remains of older diphthongs, from IE II. So, although from the point of view of the Europaio there are only stems with variants -au, -eu, -a, etc, these can all be classified as Diphthong endings, because the original stems were formed as diphthongs in the language history. This kind of irregularities is usual in today's languages, as it was already five millennia ago.

In zero grade, in Genitive, there are forms with -i- or -ij- or with -u- or -uw-, depending on the diphthongs.

SINGULAR

2. These are root words, but there is a secondary formation of words, especially that of Greek origin, in -eus, -euos, as in Avestic bazaus, arm, or gr. Basileus, which are also so declined.