(1) Destruction of an organic substance by slow combustion or gradual oxidation. (2) SYN: putrefaction. (3) To deteriorate; to undergo slow combustion or putrefaction. (4) In dentistry, caries. (5) psychology loss of information registered by the senses and processed into short-term memory.memory. (6) Loss of radioactivity with time; spontaneous emission of radiation or charged particles or both from an unstable nucleus. [L. de, down, + cado, to fall]