'ptosis' originates from Greek, specifically the word 'πτῶσις' ('ptōsis'), where the root from the verb 'πίπτω' ('piptō') meant 'to fall'.

'ptosis' entered New Latin/medical Latin as 'ptōsis' and was adopted into English as the medical term 'ptosis' in the 19th century.

Initially it meant 'a falling' in Greek, but over time it evolved into the medical sense of 'drooping or sagging of a bodily part (especially the eyelid)'.