'partygoer' originates from Modern English as a compound of 'party' + 'goer'. 'Party' comes from Old French 'partie' (meaning 'a part, division'; sense 'social gathering' developed later), and 'goer' is the agent form from the verb 'go' (Old English 'gān').

'party' changed from Old French 'partie' into Middle English 'partie' with senses including 'group' and later 'social gathering'; the agent-form '-goer' developed from the verb 'go' (Old English 'gān') plus the agentive suffix '-er', and the compound 'partygoer' arose in modern English to denote a person who goes to parties.

Initially 'party' meant 'a division or part', but over time it evolved to mean 'a social gathering'; consequently the compound 'partygoer' came to mean 'a person who attends such social gatherings'.