Dioptre
Pronunciation : Di*op"tre
Part of Speech : n.
Etymology : [F. See 2d Dioptric.] (Optics)
Definition : Defn: A unit employed by oculists in numbering glasses according to the metric system; a refractive power equal to that of a glass whose principal focal distance is one meter.
Source : Webster's Unabridged Dictionary, 1913