dioon
- n any cycad of the genus Dioon; handsome palmlike cycads with robust crowns of leaves and rugged trunks
diophantus
- n Greek mathematician who was the first to try to develop an algebraic notation (3rd century)
diopter
- n 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
dioptre
- n 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