dioptre
noun/daɪˈɒptə(r)/
/daɪˈɑːptər/
(US English diopter)
(physics)- a unit for measuring the power of a lens to refract light (= make it change direction)Word Originlate 16th cent. (originally as diopter): from French, from Latin dioptra, from Greek, from di- ‘through’ + optos ‘visible’. The term was used in the early 17th cent. to denote an ancient form of theodolite; the current sense dates from the late 19th cent.
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dioptre