DIOPTER
- a measure of refractive power, also DIOPTRE [n -S]
- unit of measure of the refractive power of a lens, having the dimension of the reciprocal of length and a unit equal to the reciprocal of one meter
- instrument, invented by Hipparchus, to measure the apparent diameter of the sun or moon or to estimate the size or elevation of distant objects
- a measure of refractive power [n DIOPTERS] : DIOPTRAL [adj]