The word 'supposing' is built upon the verb 'suppose', which entered English from Old French 'supposer'. Its core components trace back to Latin: 'sub-' (under) and 'ponere' (to place). The original Latin concept was one of placing an idea or assumption underneath a discussion as a foundation or hypothesis, often with a sense of something posited secretly or without proof. Over centuries, this concrete image of placing-under evolved into the abstract logical function of considering a proposition as true for the sake of argument. The addition of the '-ing' suffix transforms the verb into a conjunction or adjective, grammaticalizing the act of making such an assumption.

Structure: sup (under) + pos (place, put) + ing (present participle suffix) - sup: A variant of the Latin prefix 'sub-', meaning 'under', 'below', or 'secretly'. It assimilates before 'p'. - pos: From Latin 'ponere', meaning 'to place' or 'to put'. The root appears as 'pos-' in many derivatives. - ing: A present participle suffix from Old English '-ende', later '-inge', used to form verbal nouns and adjectives.