'assumedly' originates from English, specifically formed from the past participle 'assumed' (from the verb 'assume') plus the adverbial suffix '-ly'.

'assume' originates from Latin, specifically the word 'assumere,' where the prefix 'ad-' meant 'to' and the root 'sumere' meant 'to take'. Through Old French and Middle English ('assumen' / 'assume') it became the modern English verb 'assume', from which 'assumed' and then the adverb 'assumedly' were formed.

Initially, in Latin 'assumere' meant 'to take up' or 'take to oneself'; over time the sense shifted to meanings like 'take for granted' or 'suppose', and the adverb 'assumedly' has come to mean 'presumably' or 'as is assumed'.