lens (n.)

1690s, "glass to regulate light rays," from Latin lens (genitive lentis) "a lentil," on analogy of the double-convex shape. See lentil. Anatomical use, of the eye part, from 1719. Lens-cap is from 1857.

In the vernacular of the photographer, anyone crowding to the front of a group, staring into the lens, or otherwise attracting attention to himself is known as a "lens louse." ["American Photography," vol. xl, 1946; the term dates from 1915]

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Definitions of lens from WordNet
lens (n.)
a transparent optical device used to converge or diverge transmitted light and to form images;
Synonyms: lense / lens system
lens (n.)
(metaphor) a channel through which something can be seen or understood;
the writer is the lens through which history can be seen
lens (n.)
biconvex transparent body situated behind the iris in the eye; its role (along with the cornea) is to focus light on the retina;
Synonyms: crystalline lens / lens of the eye
lens (n.)
electronic equipment that uses a magnetic or electric field in order to focus a beam of electrons;
Synonyms: electron lens
Lens (n.)
genus of small erect or climbing herbs with pinnate leaves and small inconspicuous white flowers and small flattened pods: lentils;
Synonyms: genus Lens