From ὕψι "aloft", probably related to ὑπέρ "above"
ὕψος • (húpsos) (genitive ὕψεος or ὕψους); n, third declension;
- the top, summit
- high position: grandeur
This inflection pattern originally had a sigma (i.e. *ὕψεσος), 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.