'apostemation' originates from Medieval Latin, specifically the word 'apostematio' (or 'apostematio'/'apostema'), where the Greek root 'apostēma' meant 'a standing away' or 'a swelling/abscess' (from 'apo-' meaning 'away' and a root related to 'histanai' meaning 'to stand').

'apostemation' changed from the Greek word 'apostēma' into Medieval Latin 'apostematio' and later entered English in archaic or learned medical usage as 'apostemation'.

Initially, it referred more literally to a 'standing off' or swelling (a protuberance), and over time it came to be used specifically for a 'localized collection of pus' or 'abscess' in medical contexts.