o·paque / ōˈpāk/ • adj. (o·paqu·er, o·paqu·est) not able to be seen through; not transparent: the windows were opaque with steam. ∎ fig. (esp. of language) hard or impossible to understand; unfathomable: technical jargon that was opaque to her.• n. an opaque thing or substance. ∎ Photog. a substance for producing opaque areas on negatives.DERIVATIVES: o·paque·ly adv.o·paque·ness n.