Psilosis

Psilosis (/saɪˈloʊsɪs/) is the sound change in which the Greek language lost its consonant sound /h/ during antiquity. The term comes from the Greek ψίλωσις psílōsis ("smoothing, thinning out") and is related to the Greek term for smooth breathing (ψιλή psilḗ), the sign for the absence of initial /h/ in a word. Dialects that have lost /h/ are called psilotic.

The linguistic phenomenon is comparable to that of h-dropping in dialects of Modern English and to the development by which /h/ was lost in late Latin.