vergence

The story

From verge (“tend, incline”, from Latin vergere) + -ence, synonym of earlier (1660s) vergency (the equivalent of French vergence). Coined as a technical term in ophthalmology, as a hypernym of convergence and divergence, in 1902. The sense of the numeric quantity in geometric optics was introduced, from use of the term in physiological optics, in the 1920s.

First known use, by meaning

• 1902 The simultaneous turning of both eyes when focusing.
• c. 1920 A measure of convergence or divergence of rays.