'archdeaconal' originates in modern English as the adjective formed from 'archdeacon' + the suffix '-al' (forming adjectives meaning 'relating to').

'archdeacon' (the root) comes from Medieval Latin 'archidiaconus' and Old French 'archedechon', ultimately from Greek 'archidiákonos' ('archi-' + 'diákonos'), and the English adjective 'archdeaconal' developed by adding the adjectival suffix '-al' to the English noun.

Initially it meant 'of or relating to an archdeacon' and over time this ecclesiastical meaning has remained essentially the same in modern usage.