'fever-causer' is a modern English compound formed from 'fever' + 'causer'. 'fever' originates from Old English 'fēfor' and ultimately from Latin 'febris', where 'febris' meant 'fever'. 'causer' derives from the verb 'cause', which comes from Old French 'cause' and Latin 'causa', where 'causa' meant 'reason' or 'cause'.

'fever' existed in Old English as 'fēfor' and continued into Middle and Modern English as 'fever'; 'cause' entered English via Old French 'cause' from Latin 'causa'. The descriptive compound 'fever-causer' is formed in modern English by combining these elements to denote an agent that causes fever.

Individually, 'fever' referred to the medical condition and 'cause' to a reason or source; when combined in modern usage the compound specifically denotes 'an agent that produces fever'.