Noun
(physiology) The simultaneous turning of both eyes when focusing. [1902]
(optics) A measure of convergence or divergence of rays. [c. 1920]
1921, The Optician and Scientific Instrument Maker, volume 62, page 1:
1947 Benjamin King Johnson, Optics and Optical Instruments: An Introduction with Special Reference to Practical Applications, Courier Corporation (1960 [1947]), p. 152.
(geology) The direction of the overturned component of an asymmetric fold.
Source: en.wiktionary.org