'atretic' originates from Greek via medical Latin/modern medical usage, ultimately related to 'atresia' which combines the prefix 'a-' meaning 'not' and the Greek root related to a hole or perforation (from Greek τρῆμα / 'trēma', 'hole').

'atretic' derives from Medieval/Modern Latin 'atresia' (medical Latin), which itself comes from Greek formation 'a-' + 'trēma' (hole, perforation); the adjective form 'atretic' developed in English through 19th-century medical usage to describe conditions of closure or absence.

Initially built from elements meaning 'without a hole' (absence of an opening); over time it came to be used in medicine and biology to mean 'closed, undeveloped, or degenerating,' especially of organs or tissues.