decay

(noun): The process or result of being gradually decomposed.
(noun): A deterioration of condition; loss of status or fortune.
(verb): To deteriorate, to get worse, to lose strength or health, to decline in quality.
(verb): (of organic material) To rot, to go bad.
(verb): (of an unstable atom) To change by undergoing fission, by emitting radiation, or by capturing or losing one or more electrons.
(verb): (of a quantum system) To undergo optical decay, that is, to relax to a less excited state, usually by emitting a photon or phonon.
(verb): Loss of airspeed due to drag.
(verb): To cause to rot or deteriorate.

The pair loved to take pictures in the decaying hospital on forty-third street.
The cat's body decayed rapidly.
The extreme humidity decayed the wooden sculptures in the museum's collection in a matter of years.