verb
1.
to pass from a higher to a lower type or condition
the road quickly deteriorated into a bumpy path
Synonyms: decline, degenerate, descend, disimprove, disintegrate, retrograde, rot, sink, worsen
Related Word: crumble, decay, decompose; impair, mar, spoil; debilitate, undermine, weaken; depreciate, lessen
Idioms: be the worse for wear, go downhill, go to pot ( or the dogs)
Contrasted words: better, improve; advance, progress; enhance, heighten
Antonyms: ameliorate
2.
Synonyms: fail 1, decline, ||dwine, fade, flag, languish, weaken