n.
Pronunciation: d ī - ' äp-t ə r, ' d ī - ˌ äp-
Function: noun
Etymology: diopter (an optical instrument), from Middle French dioptre, from Latin dioptra, from Greek, from dia- + opsesthai to be going to see ― more at OPTIC
Date: circa 1864
: a unit of measurement of the refractive power of lenses equal to the reciprocal of the focal length in meters