Psilosis

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