Definition of decline noun from the Oxford Advanced American Dictionary

    

decline

 noun
noun
NAmE//dɪˈklaɪn//
 
[countable, usually singular, uncountable]decline (in something)decline (of something)
 
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 a continuous decrease in the number, value, quality, etc. of something a rapid/sharp/gradual decline urban/economic decline The company reported a small decline in its profits. An increase in cars on the roads has resulted in the decline of public transport. The town fell into (a) decline (= started to be less busy, important, etc.) after the mine closed. The steel industry in the United States has been in decline since the 1970s.
See the Oxford Advanced Learner's Dictionary entry: decline