General English

  • noun the natural process of going bad or of becoming damaged, e.g. when things are not looked after properly
  • verb to go bad or to become damaged in this way

General Science

  • noun the formation of dental caries in teeth


  • noun a process by which tissues become rotten and decompose, caused by the action of microorganisms and oxygen


  • noun the process of a sound signal fading away



  • A gradual decrease in the magnitude of a quantity, such as current, voltage, luminescence, or magnetic flux.
  • The spontaneous disintegration of unstable atomic nuclei, such as those of uranium or curium, mainly through the emission of alpha, beta, or gamma rays. Also called disintegration (2), or radioactivity (1).
  • A specific instance of decay (2), such as that occurring when an atom of uranium-238 emits an alpha particle to form an atom of thorium-234. Also called disintegration (3), or radioactivity (2).
  • The reduction over time of the radioactivity of a substance, due to decay (2). Also called disintegration (4), or radioactivity (3).
  • synonymdisintegration


  • noun damage caused to tissue or a tooth by the action of microorganisms, especially bacteria

Origin & History of “decay”

The notion underlying decay and its close relative decadence is of a ‘falling off’ from a condition of health or perfection. Decay comes from Old Northern French decair, a descendant of vulgar Latin *dēcadere, which in turn came from Latin dēcidere, a compound verb formed from the prefix - ‘down, off, away’ and cadere ‘fall’ (source of English case and a wide range of related words). Decadence (16th c.) was acquired via the medieval derivative dēcadentia.

To the same word-family belongs deciduous (17th c.), from Latin dēciduus, literally denoting the ‘falling off’ of leaves from trees.