Either from ὄρνυμι (ornumi, “I raise”), or possibly directly from a Proto-Indo-European *h₃eros. Compare Sanskrit ऋष्व (ṛṣvá).
ὄρος • (oros) (genitive ὄρεος, ὄρους) n, third declension
- a mountain, hill
- mountain chain
- district, sector, precinct, parish
This inflection pattern originally had a sigma (i.e. ὄρεσος), which was dropped early on in the history of Ancient Greek.
The irregular accentuation of this paradigm is explained by the fact that it is the contracted version of the above paradigm.
- English: oro-
- Greek: όρος m (óros, “mountain”)