Meaning of “decline” - Learner’s Dictionary

decline

verb uk us /dɪˈklaɪn/
REFUSE [ I, T ] formal

B2 If you decline something, you refuse it politely:

She declined his offer of a lift.
[ + to do sth ] He declined to comment.
BECOME LESS [ I ]

B2 to become less in amount, importance, quality, or strength:

Sales of records have declined steadily.

(Definition of “decline verb” from the Cambridge Learner’s Dictionary © Cambridge University Press)