Ybos
From Simon Online
Ybos grece gibbus yuos dicunt.
Apparatus:
gibbus AC e | gibbus sʒ f | gilbus B {'bb' misread as 'lb'}
Translation:
Ybos is Greek for Latin gibbus {"hunched, humped"}; and the Greeks pronounce it yvos.
Commentary:
Greek ὑβός /hybós/ means "humpbacked". The medieval Greek pronunciation is /ivós/ showing loss of /h/, /b/ > /v/, and /y/ > /i/. Simon's spelling with 'y' happens to be etymological but it could just as well have been with 'i' making no difference to the pronunciation.