—decayable, adj. —decayedness /di kayd"nis, -kay"id-/, adj. —decayless, adj./di kay"/, v.i.1. to become decomposed; rot: vegetation that was decaying.2. to decline in excellence, prosperity, health, etc.; deteriorate.3. Physics. (of a radioactive nucleus) to change spontaneously into one or more different nuclei in a process in which atomic particles, as alpha particles, are emitted from the nucleus, electrons are captured or lost, or fission takes place.v.t.4. to cause to decay or decompose; rot: The dampness of the climate decayed the books.n.5. decomposition; rot: Decay made the wood unsuitable for use.6. a gradual falling into an inferior condition; progressive decline: the decay of international relations; the decay of the Aztec civilizations.7. decline in or loss of strength, health, intellect, etc.: His mental decay is distressing.8. Also called disintegration, radioactive decay. Physics. a radioactive process in which a nucleus undergoes spontaneous transformation into one or more different nuclei and simultaneously emits radiation, loses electrons, or undergoes fission.9. Aerospace. the progressive, accelerating reduction in orbital parameters, particularly apogee and perigee, of a spacecraft due to atmospheric drag.[1425-75; (v.) late ME decayen < ONF decair, equiv. to de- DE- + cair to fall < VL *cadere, for L cadere; (n.) late ME, deriv. of the v.]Syn. 1. degenerate, wither; putrefy. DECAY, DECOMPOSE, DISINTEGRATE, ROT imply a deterioration or falling away from a sound condition. DECAY implies either entire or partial deterioration by progressive natural changes: Teeth decay. DECOMPOSE suggests the reducing of a substance to its component elements: Moisture makes some chemical compounds decompose. DISINTEGRATE emphasizes the breaking up, going to pieces, or wearing away of anything, so that its original wholeness is impaired: Rocks disintegrate. ROT is a stronger word than DECAY and is esp. applied to decaying vegetable matter, which may or may not emit offensive odors: Potatoes rot. 5. putrefaction. 7. deterioration, decadence, impairment, dilapidation, degeneration.
* * *(as used in expressions)tooth decay
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