deteriorate

Synonyms: adulterate alloy become worse be worse for wear break corrode corrupt crumble debase debilitate decline decompose degrade deprave depreciate descend disimprove disintegrate ebb fade fail fall apart flag go downhill go to pieces go to pot go to the dogs hit the skids impair injure languish lapse lessen lose it lose quality lower mar pervert regress retrograde retrogress rot sink skid slide spoil undermine vitiate weaken wear away worsen

Antonyms: build construct develop get better improve