—n. 1. a piece of transparent substance, usually glass, having two opposite surfaces either both curved or one curved and one plane, used in an optical device in changing the convergence of light rays, as for magnification, or in correcting defects of vision.
2. a combination of such pieces.
3. some analogous device, as for affecting sound waves, electromagnetic radiation, or streams of electrons.
4. Anat.See crystalline lens. 5. Geol.a body of rock or ore that is thick in the middle and thinner toward the edges, similar in shape to a biconvex lens.