'antecedently' originates from Latin, specifically the verb 'antecedere', where 'ante-' meant 'before' and 'cedere' meant 'to go'.

'antecedere' passed into Medieval Latin as 'antecedent-' (meaning 'going before' or 'preceding') and then into English as the adjective and noun 'antecedent'; the adverb 'antecedently' was formed in English by adding the suffix '-ly'.

Initially it referred to the action 'to go before' or something that 'goes before'; over time it came to mean 'occurring or existing before in time, order, or cause', which is its modern usage.