lens Definition

lens
noun lenses

1a. An optical device consisting of a piece of glass, clear plastic, etc curved on one or both sides, used for converging or diverging a beam of light;

Thesaurus: eye, eyepiece, eyeglass, glass.
1b. A contact lens.
2. In the eye of many vertebrates, including humans: the transparent biconvex structure behind the iris which focuses light from an object on to the retina, forming an image.

Form: crystalline lens (technically also)
3. In a camera: a mechanical equivalent of the lens of an eye which allows the image to fall on the photographer's eye or, when the shutter is open, on the film plane. See also fish-eye lens, telephoto lens, wide-angle lens.

Etymology: 17c: Latin, meaning ‘lentil' (because of the shape).