'archchaplain' originates from Medieval Latin, specifically the compound 'archi-cappellanus', where 'archi-' meant 'chief' (from Greek 'arkhi-') and 'cappellanus' meant 'chaplain' (from Late Latin 'capellanus' related to 'cappa' meaning 'cape' or 'cloak').

'archi-cappellanus' in Medieval Latin passed into Old French/Anglo-Norman forms (e.g. 'archchapelain'/'archchaplain') and was adopted into Middle English as 'archchaplain', eventually becoming the modern English 'archchaplain'.

Initially it meant 'chief of the chapel' or 'principal chaplain' in a literal, institutional sense; over time the term retained that core meaning but became more of a formal title in historical contexts rather than a common occupational label.