A right line drawn or extending from the center of a circle to the periphery; the semidiameter of a circle or sphere. [1913 Webster]
The preaxial bone of the forearm, or brachium, corresponding to the tibia of the hind limb. See Illust. of Artiodactyla. [1913 Webster]
" The radius is on the same side of the limb as the thumb, or pollex, and in man it is so articulated that its lower end is capable of partial rotation about the ulna." [1913 Webster]
A ray, or outer floret, of the capitulum of such plants as the sunflower and the daisy. See Ray, 2. [1913 Webster]
The barbs of a perfect feather. [1913 Webster]
The movable limb of a sextant or other angular instrument. Knight. [1913 Webster]

Radius bar (Mach.), a bar pivoted at one end, about which it swings, and having its other end attached to a piece which it causes to move in a circular arc. -- Radius of curvature. See under Curvature.

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OXFORD DICTIONARY

radius, n. & v.
--n. (pl. radii or radiuses)
1 Math. a a straight line from the centre to the circumference of a circle or sphere. b a radial line from the focus to any point of a curve. c the length of the radius of a circle etc.
2 a usu. specified distance from a centre in all directions (within a radius of 20 miles; has a large radius of action).
3 a the thicker and shorter of the two bones in the human forearm (cf. ULNA). b the corresponding bone in a vertebrate's foreleg or a bird's wing.
4 any of the five arm-like structures of a starfish.
5 a any of a set of lines diverging from a point like the radii of a circle. b an object of this kind, e.g. a spoke.
6 a the outer rim of a composite flower-head, e.g. a daisy. b a radiating branch of an umbel.
--v.tr. give a rounded form to (an edge etc.).

Idiom

radius vector Math. a variable line drawn from a fixed point to an orbit or other curve, or to any point as an indication of the latter's position.

Etymology

L, = staff, spoke, ray

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THESAURUS

radius

O, air line, ambit, amplitude, annular muscle, annulus, approach, area, areola, asymptote, aureole, axis, beeline, bigness, body, bore, bottleneck, breadth, bulk, caliber, carry, chaplet, chord, circle, circuit, circumference, circus, closed circle, collision course, compass, concentralization, concentration, concourse, concurrence, confluence, conflux, congress, convergence, converging, corona, coronet, coverage, crossing, crown, cycle, depth, diadem, diagonal, diameter, diapason, diffusion, dimension, dimensions, direct line, directrix, discus, disk, dispersion, edge, emanation, eternal return, expanse, expansion, extension, extent, fairy ring, focalization, focus, funnel, gamut, garland, gauge, girth, glory, great-circle course, greatness, halo, height, hub, largeness, lasso, length, logical circle, loop, looplet, magic circle, magnitude, mass, measure, measurement, meeting, mutual approach, narrowing gap, noose, normal, orbit, perpendicular, proportion, proportions, purview, radiance, radiation, radius vector, range, ray, reach, register, right line, ring, rondelle, round, roundel, saucer, scale, scattering, scope, secant, segment, semidiameter, shortcut, side, size, spectrum, sphincter, spoke, spokes, spread, straight, straight course, straight line, straight stretch, straightaway, streamline, stretch, sweep, tangent, transversal, vector, vicious circle, volume, wheel, width, wreath

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ROGET THESAURUS

radius

Length

N length, longitude, span, mileage, distance, line, bar, rule, stripe, streak, spoke, radius, lengthening, prolongation, production, protraction, tension, tensure, extension, line, nail, inch, hand, palm, foot, cubit, yard, ell, fathom, rood, pole, furlong, mile, league, chain, link, arpent, handbreadth, jornada, kos, vara, astronomical unit, AU, light- year, parsec, nanometer, nm, micron, micrometer, millimicron, millimeter, mm, centimeter, cm, meter, kilometer, km, pedometer, perambulator, scale, long, longsome, lengthy, wiredrawn, outstretched, lengthened, sesquipedalian, interminable, no end of, macrocolous, linear, lineal, longitudinal, oblong, as long as my arm, as long as today and tomorrow, unshortened &c (shorten), lengthwise, at length, longitudinally, endlong, along, tandem, in a line, in perspective, from end to end, from stem to stern, from head to foot, from the crown of the head to the sole of the foot, from top to toe, fore and aft.

Thickness,

N breadth, thickness, breadth, width, latitude, amplitude, diameter, bore, caliber, radius, superficial extent, thickness, crassitude, corpulence, dilation, broad, wide, ample, extended, discous, fanlike, outspread, outstretched, wide as a church-door, latifoliate, latifolous, thick, dumpy, squab, squat, thickset, thick as a rope.

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