■ verb
1》 rot or cause to rot through the action of bacteria and fungi; decompose.
↘decline in quality or vigour; deteriorate.
2》 Physics (of a radioactive substance, particle, etc.) undergo change to a different form by emitting radiation.
■ noun
1》 the state or process of ~ing.
2》 rotten matter or tissue.
Origin
ME: from OFr. decair , based on L. decidere 'fall down or off', from de- 'from' + cadere 'fall'.