'post' originates from Latin, specifically the word 'post', where 'post' meant 'after'. 'fever' originates from Old English, ultimately from Latin 'febris' (via Old French 'fievre'), where 'febris' meant 'fever'.

'post-fever' is a modern English compound formed by adding the Latin-derived prefix 'post-' to the noun 'fever'. 'fever' changed from Old English forms and Old French 'fievre' (from Latin 'febris') and eventually became the modern English word 'fever'; the compound usage using 'post-' to indicate 'after' developed in Modern English.

Initially, the elements meant simply 'after' ('post-') and 'fever' ('febris' = 'fever'); combined, the term originally meant 'after a fever' and has remained a descriptive term for the period or conditions following a fever, with increasing use in clinical descriptions of post-febrile symptoms.