From Latin 'in-' (upon) + 'pōnere' (to place) — literally 'to place upon,' also giving us 'impostor.'
To establish or apply something as compulsory; to force something unwelcome on someone; to take unfair advantage of someone's generosity.
From Old French 'imposer' (to lay upon, to inflict), a Romance remodeling of Latin 'impōnere' (to place upon, to set over), from 'in-' (into, upon) and 'pōnere' (to put, to place). The literal meaning is 'to put upon' — to place a burden, obligation, or authority on someone or something. The sense of deceiving ('imposing on' someone's credulity) appeared by the 16th century, and the related noun 'impostor' comes from the same Latin verb. Key roots: pōnere / positum (Latin: "to put, to place"), in- (Latin: "in, into, upon").
The word 'impostor' comes from the same Latin verb 'impōnere' — literally, one who 'places upon' others a false identity. In late Latin, 'impostōrem' meant a deceiver, someone who imposes a fiction on the world. The modern 'impostor syndrome,' coined by psychologists in 1978, thus literally describes feeling like someone who has placed a false self upon the world.