n. In mathematics, one of a number of lines proceeding from a center; a ray; especially, a line drawn from the center to the periphery of a circle or sphere; also, the measure of the semidiameter.n. In anatomy and zoology, the outer one of the two bones of the forearm, or corresponding part of the fore leg; the bone on the thumb side of the forearm, extending from the humerus to the carpus, and bearing upon its distal end the manus or hand: so called from its revolving, somewhat like a spoke, about the ulna, as in man and other mammals whose fore limb exhibits the motions called pronation and supination.n. In ichthyology, a bone of the pectoral arch, wrongly identified by some naturalists with the radius of higher vertebrates. The one so called by Cuvier is the hypercoracoid, and that of Owen is the hypocoracoid.n. In entomology, a vein of the wing of some insects, extending from the pterostigma to the tip of the wing.n. In conchology, a genus of Ovulidæ. R. volra is the shuttle-shell or weaver-shell.n. plural In ornithology, the barbs of the main shaft of a feather; the rays of the first order of the rachis.n. In arachnology, one of the radiating lines of a geometrical spider's web, which are connected by a single spiral line.n. In echinoderms, one of the five radial pieces of the dentary apparatus of a sea-urchin, being an arched rod-like piece articulated at its base with the inner extremity of each rotula, running more or less nearly parallel with the rotula, and ending in a free bifurcated extremity. Also called the compass of the lantern of Aristotle (which see, under lantern). See also cut B under lantern.n. plural Specifically, in Cirripedia, the lateral parts of the shell, as distinguished from the paries, when they overlap: when overlapped by others, they are called alæ.n. In botany, a ray, as of a composite flower, etc.n. The movable limb or arm of a sextant; also, a similar feature in any other instrument for measuring angles.n. In fortification, a line drawn from the center of the polygon to the end of the outer side.n. One of the principal longitudinal veins in an insect's wing, between the subcosta and the præmedia. It is vein III of Comstock's system.