de·com·pose / ˌdēkəmˈpōz/ • v. [intr.] (of a dead body or other organic matter) decay; become rotten: [as adj.] (decomposed) the body was decomposed. ∎  [tr.] cause (something) to decay or rot. ∎  (of a chemical compound) break down into component elements or simpler constituents. ∎  [tr.] break down (a chemical compound) into its component elements or simpler constituents.DERIVATIVES: de·com·pos·a·ble adj.de·com·po·si·tion / dēˌkämpəˈzishən/ n.

decompose separate into its parts; decay. XVIII. — F. décomposer, f. DE- 6 + composer COMPOSE.
So decomposition XVII.