| radii |
a plural form of radius. |
| radio |
the sending of communications by means of electromagnetic waves in the frequency range from ten kilocycles to three hundred thousand megacycles. [9 definitions] |
| radioactive |
emitting energy or subatomic particles as a result of the decay of unstable isotopes. [2 definitions] |
| radioactivity |
the emission or amount of emission of energy or subatomic particles by the nuclei of certain unstable isotopes of elements as they decay. |
| radish |
one of a group of herbs of the cabbage family that have a pungently flavored, crisp, edible root. [2 definitions] |
| radium |
a radioactive chemical element that has eighty-eight protons in each nucleus and that occurs in pure form as a solid metal, used esp. as a radiation source for cancer treatment. (symbol: Ra) |
| radius |
a straight line segment extending from the center to the surface of a sphere or from the center to the circumference of a circle. [7 definitions] |
| radon |
a radioactive chemical element of the inert gas group that has eighty-six protons in each nucleus and that is produced by the radioactive decay of trace amounts of radium in the soil. (symbol: Rn) |
| raffle |
a type of lottery in which participants buy tickets, one of which is drawn to determine the prizewinner. [2 definitions] |
| raft1 |
a flat platform made of buoyant materials such as wood or air-filled barrels, designed to float and often to support or carry people or goods. [6 definitions] |
| rag1 |
a scrap or fragment of cloth. [5 definitions] |
| rag2 |
(informal) to tease or scold. |
| rage |
intense anger; fury. [8 definitions] |
| ragged |
worn down into rags; torn and tattered. [5 definitions] |
| ragtime |
a late nineteenth and early twentieth-century American musical form, having a syncopated melody and an accompaniment in two-four time, usu. written for the piano. |
| ragweed |
a weed of the daisy family that produces abundant airborne pollen in the fall. |
| raid |
a sudden or surprise attack or assault, as by a military force. [7 definitions] |
| rail1 |
a horizontal bar that extends between two posts and serves as a barrier, fence, or the like. [4 definitions] |
| railing |
a barrier or fence made of posts and rails. [3 definitions] |
| railroad |
a road of parallel steel rails upon which railway cars travel. [5 definitions] |
| railway |
a railroad system, esp. one operating over short distances using light equipment. [2 definitions] |