1 [no object] : to become worse as time passes

• The weather gradually deteriorated as the day went on.
• Her health continues to deteriorate.
• efforts to save a deteriorating rain forest
• The disagreement deteriorated into a fight.

2 [+ object] : to make something worse

• Exposure to rain and sun will gradually deteriorate the paint.

— deteriorated adjective

• a deteriorated building
• a badly deteriorated part of the city