What is Decline ?
Decline is (noun) the fact of going downwards a welcome decline in the number of cases of pollution Sales figures have gone into a sharp decline. Synonym deterioration (verb) 1. to refuse or to turn down an invitation or offer She declined their request. He declined to come to lunch. 2. to become weaker He declined rapidly after he went into hospital. 3. to become less in numbers or amount Our sales declined over the last year. The fish population has declined sharply.
source: Easier English, Student Dictionary Upper Intermediate Level