{ Di‐op″ter (?), ‖Di‐op″tra (?), } n. [L. dioptra, fr. Gr. �. See 2d Dioptric.] An optical instrument, invented by Hipparchus, for taking altitudes, leveling, etc.
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Webster's Dictionary 1913
Webster's Revised Unabridged Dictionary, C. & G. Merriam Co., 1913.