Decay, decompose, rot, putrefy, spoil, disintegrate, crumble mean to undergo or, in some cases, to cause something to undergo destructive dissolution.
Decay implies change, commonly a natural and gradual change, from a state of soundness or perfection; it may or may not suggest the certainty of complete destruction.
Decompose stresses the idea of breaking down by separation into constituent parts or elements (as by chemical action in the laboratory or, in respect to animal and vegetable matter in nature, by the action of living microorganisms).
Rot implies decay and decomposition, usually of or as if of animal or vegetable matter; the term may or may not imply offensiveness or foulness; figuratively it differs from decay in stressing stagnation or corruption rather than decline.
Putrefy not only suggests the rotting of or as if of animal matter but also stresses its extreme offensiveness to sight and smell.
Spoil (see also INJURE) is often used in place of decay, rot, or putrefy when foodstuffs, especially in the home or the market, are referred to.
Disintegrate implies either a breaking down or a breaking apart so that the wholeness or integrity of the thing or the cohesiveness of its particles is destroyed or is in process of destruction.
Crumble implies disintegration of or as if of a substance that breaks into fine particles; neither it nor disintegrate need imply, as the remaining terms almost inevitably do, an alteration at the chemical level.