vergency

verge + -ency, cf. New Latin vergentia (16th century), French vergence (18th century) and later English vergence (20th century).

vergency (plural vergencies)

1. (dated) The act of verging or approaching; tendency, inclination towards something. [1668]

   1668 John Wilkins, An Alphabetical Dictionary: Wherein All English Words According to Their Various Significations, are Either Referred to Their Places in the Philosophical Tables, Or Explained by Such Words as are in Those Tables, J.M.

   • s.v. hanker: "vergency, incline"

   1704 Plutarch's Morals, vol. 3, Thomas Braddyll, London, p. 155.

   • "the Earth is moved about the Sun by its Inclination and Vergency towards it"

   1721 Nathan Bailey, An Universal Etymological English Dictionary, E. Bell, London.

   • "VERGENCY [of vergere, L.] a bending or declining away, from or to, inclining."

2. The reciprocal of the focal distance of a lens, used as a measure of the divergence or convergence of a pencil of rays.
   • 1863, The Civil Engineer and Architect's Journal:

     When, by the pencil becoming oblique to the surface, the vergency produced on the pencil becomes changed, the primary and secondary focal points, V and H, separate […]

• vergence