breathing mark
diacritical mark in Ancient Greek that appears above or before initial vowels and diphthongs to indicate either the presence (rough breathing) or absence (smooth breathing) of an 'h' sound at the beginning of the word
en-GB/ˈbɹiːðɪŋ ˈmɑːk/
en-US/ˈbɹiðɪŋ ˈmɑɹk/