-nsē, -si noun
( -es )
Etymology: verge (III) + -ency
1. obsolete : the act or process of verging, approaching, or bordering on something : tendency , inclination
2. : a measure of convergence or divergence of a pencil of rays entering or issuing from a lens or mirror that is expressed as the reciprocal of the distance from lens or mirror to the focus of the rays and for rays through a principal focus is equal to the focal power of the lens or mirror