From the traditional Ashkenazi pronunciation of Hebrew ־וֹת (“-ót”), and its Yiddish [Term?] reflex.
From Latin -ōsus.
The Esperanto suffixes -as, -is, -os, -us are related, and appear to have been inspired by previous language projects:
- This play of vowels is not an original idea of Zamenhof's: -as, -is, -os are found for the three tenses of the infinitive in Faiguet's system of 1765; -a, -i, -o without a consonant are used like Z's -as, -is, -os by Rudelle (1858); Courtonne in 1885 had -am, -im, -om in the same values, and the similarity with Esperanto is here even more perfect than in the other projects, as -um corresponds to Z's -us. —An International Language (1928)
Borrowed from Esperanto -os, back-formation from -as.
From Latin -ōsus (“full (of)”).