Meaning

noun a transparent optical device used to converge or diverge transmitted light and to form images

noun (metaphor) a channel through which something can be seen or understood

noun biconvex transparent body situated behind the iris in the eye; its role (along with the cornea) is to focuses light on the retina

originBorrowed from Latin lēns (“lentil”), with Medieval Latin later taking on the sense of “lens”, a semantic loan from Arabic عَدْسَة (ʕadsa, “lentil; optic lens”); the similar shape is the common factor.

Etymology from Wiktionary, CC BY-SA 3.0