decay

> decay
(verb)
decline, deteriorate, disintegrate, fail, perish, wane, waste, wither.
decompose, putrefy, rot.

> decay
(noun)
caducity, decadence, declension, decline, decomposition, decrepitude, degeneracy, degeneration, deterioration, dilapidation, disintegration, fading, failing, perishing, putrefaction, ruin, wasting, withering.