| opaque | Impervious to light; not translucent or only slightly so. Compare: radiopaque. Origin: Fr. Fr. L. Opacus, shady (05 Mar 2000) |
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| opaque microscope | <instrument> A microscope with a condenser built around the objective; used for the investigation of opaque, or only slightly translucent, minute specimens. Synonym: opaque microscope. (05 Mar 2000) |