lens

Concise Oxford English Dictionary © 2008 Oxford University Press:
lens/lenz/

▶noun

• 1 a piece of glass or other transparent material with one or both sides curved for concentrating or dispersing light rays.

  ■ Anatomy the transparent elastic structure behind the iris by which light is focused on to the retina of the eye.

  ■ short for contact lens.

• 2 the light-gathering device of a camera, containing a group of compound lenses.

• 3 Physics an object or device which focuses or otherwise modifies a beam of radiation, sound, electrons, etc.

– derivatives
lensed adjective,
lensless adjective.

– origin C17: from L., ‘lentil’ (because of the similarity in shape).