Real Dictionary

lens
countable noun: A lens is a thin curved piece of glass or plastic used in things such as cameras, telescopes, and pairs of glasses. You look through a lens in order to make things look larger, smaller, or clearer.

lens in American English
a piece of glass, or other transparent substance, with two curved surfaces, or one plane and one curved, regularly bringing together or spreading rays of light passing through it: a lens or combination of lenses is used in optical instruments, eyeglasses,
to photograph
noun: 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
transitive verb: to film (a motion picture)

lens in British English
noun: a piece of glass or other transparent material, used to converge or diverge transmitted light and form optical images
noun: an industrial town in N France, in the Pas de Calais department; badly damaged in both World Wars. Pop: 36 257 (2006)