From Proto-Indo-European *obʰelos, from *h₃bʰel- (whence also ὀφείλω (opheílō)). Cognates include Old Armenian աւելի (aweli, “more”), յաւելում (yawelum, “I add”).
ὄφελος • (óphelos) (genitive ὀφέλους) n, third declension
- furtherance, advantage, help, good, benefit
- the best
- (+ dative) help against something
This inflection pattern originally had a sigma (i.e. ὀφέλεσος), 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.