n.1 a piece of a transparent substance with one or (usu.) both sides curved for concentrating or dispersing light-rays esp. in optical instruments.
2 a combination of lenses used in photography.
3 Anat. crystalline lens.
4 Physics a device for focusing or otherwise modifying the direction of movement of light, sound, electrons, etc.
Derivatives:
lensed adj. lensless adj.
Etymology: L lens lentis lentil (from the similarity of shape)