Suppose
Middle English: from Old French supposer, from Latin supponere (from sub- ‘from below’ + ponere ‘to place’), but influenced by Latin suppositus ‘set under’ and Old French poser ‘to place’.
wiktionary
From Middle English supposen, borrowed from Old French supposer, equivalent to prefix sub-(“under”) + poser(“to place”); corresponding in meaning to Latin supponere(“to put under, to substitute, falsify, counterfeit”), suppositum. See pose.
etymonline
suppose (v.)
early 14c., "to assume as the basis of argument," from Old French suposer "to assume" (13c.), probably a replacement (influenced by Old French poser "put, place") of *suppondre, from Latin supponere "put or place under; to subordinate, make subject," from assimilated form of sub "under" (see sub-) + ponere "put, place" (past participle positus; see position (n.)). Meaning "to admit as possible, to believe to be true" is from 1520s.
