These words refer to the breakdown of dead organic tissues by natural bacterial processes. Rot is the least formal and most forceful of these words, suggesting an advanced point in this process of breakdown; the tissues at his point might or might not be foul-smelling but they would in any case be almost unrecognizable, compared to their former state: a fear of plague that had left dead bodies to rot in the streets; a snail that had completely rotted away inside its shell: leather bindings that had rotted to pieces in the damp basement; leaves left to rot in the compost heap. Spoil , by contrast, refers to an earlier point in the process of organic breakdown; it is especially applied to foods that have turned "bad" or begun to turn: milk that had spoilt out of the refrigerator; drying fruit in the sun so that it would not spoil .

Decay is a more matter-of-fact word than rot , and applies generally to the whole process of breakdown, but particularly to the end point of total destruction: a corpse that had already decayed , leaving only the skeleton intact; washed-up seaweed that lay decaying on the beach. Decompose is a more formal substitute for decay , but is almost clinical in its particular reference to a stage in the process between spoil and rot where tissues may be distended and ruptured by a build-up of gases: formaldehyde to prevent the specimens from decomposing ; treatment plants to decompose sewage more rapidly.

Putrefy refers to the same point in the process as decompose , stressing particularly the presence of foul or poisonous gases and noxious odours: fish that had died and now lay putrefying in the shallows of the stream; garbage that putrefied in heaps on the neglected beach. Moulder might now be thought too precious or euphemistic a substitute for decay. It means to decay gradually and turn into dust: his remains mouldering in the tomb; old castles mouldering on the Rhine.