dioptre

Noun

di=op=tre

WORDNET DICTIONARY

dioptre(n = noun.quantity) diopter - a unit of measurement of the refractive power of a lens which is equal to the reciprocal of the focal length measured in meters; used by oculists;

is a kind of unit, unit of measurement

dioptre, n. (US diopter) Optics a unit of refractive power of a lens, equal to the reciprocal of its focal length in metres.

Etymology

F dioptre f. L dioptra f. Gk dioptra: see DIOPTRIC