(anatomy) The long bone in the forearm, on the side of the thumb. / (zoology) The lighter bone (or fused portion of bone) in the forelimb of an animal.

(computing) Initialism of Remote Authentication Dial-In User Service.

(mathematics, for any point on a curve) The radius of the osculating circle at the point on the curve

(hydraulics, surface science) For a porous material, the ratio of porosity (ratio of volume of interstitial space filled with fluid to volume of material) to specific surface area (ratio of surface area in contact with fluid to volume of material); for a pipe or channel, the ratio of cross-sectional area to wetted perimeter.

(astronomy) The radius of an object such that, if all its mass were compressed within that radius, the escape velocity would equal the speed of light.

(firearms) The distance between the front and rear sights of a firearm.

plural of radius vector

(mathematics) A straight line (or the length of such line) connecting any point, as of a curve, with a fixed point, or pole, round which the straight line turns, and to which it serves to refer the successive points of a curve, in a system of polar coordinates.

(informal, astronomy) The radius of a celestial body when it is long enough to allow gravity to transform the body into a globe, typically estimated at approximately 300 kilometres.

(physics, chemistry) The distance between the proton and electron of hydrogen atom in its ground state