decay - an inferior state resulting from the process of decaying; "the corpse was in an advanced state of decay"; "the house had fallen into a serious state of decay and disrepair"

corrosion - a state of deterioration in metals caused by oxidation or chemical action

desolation, devastation - the state of being decayed or destroyed

decrepitude, dilapidation - a state of deterioration due to old age or long use

wear - impairment resulting from long use; "the tires showed uneven wear"

decline, diminution - change toward something smaller or lower

drop-off, falling off, falloff, slump, slack - a noticeable deterioration in performance or quality; "the team went into a slump"; "a gradual slack in output"; "a drop-off in attendance"; "a falloff in quality"