Lens, from the Latin, lens, the lentil bean.
The lens of the eye was so named by the Romans in the 1st century B.C. because of its resemblance to a lentil bean in shape and size.
The diameter of the human lens at birth is about 6 mm. By the time one is in their mid-sixties the lens will typically have reached a maximum diameter of around 9 mm. (The average diameter of a lentil is 6-7 mm.)