'assumptive' originates from Latin, specifically the word 'assumptivus', where 'assumere' (from 'ad-' + 'sumere') meant 'to take up' ('ad-' meant 'toward' and 'sumere' meant 'to take').

'assumptive' was formed in English from the Latin past-participial root 'assumptus' / adjective-forming elements (via Late Latin 'assumptivus') and the English suffix '-ive', developing through Medieval and Early Modern English formations related to 'assumption'.

Initially related to 'taking up' or 'taking on' (the literal sense from Latin), the word evolved to mean 'based on assumption' and, by extension, 'presumptuous' (making unwarranted assumptions).