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(Units) a unit for measuring the refractive power of a lens: the reciprocal of the focal length of the lens expressed in metres
[C16: from Latin dioptra optical instrument, from Greek, from dia- through + opsesthai to see]
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|Noun||1.||dioptre - 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|