n. 1 a a straight line passing from side to side through the centre of a body or figure, esp. a circle or sphere. b the length of this line. 2 a transverse measurement; width, thickness. 3 a unit of linear measurement of magnifying power (a lens magnifying 2000 diameters). diametral adj.
[ ME f. OF diametre f. L diametrus f. Gk diametros (gramme) (line) measuring across f. metron measure ]