Other forms: declined, declining, declines
To decline is to politely say no to an offer. Decline the invitation, respectfully decline, he declined to comment.
It is the formal and courteous refusal. Declined to comment is the standard news formula for somebody who was asked and said nothing. The other main sense is to fall or get worse: numbers declined, declining health — and as a noun, a decline is that fall: a decline in numbers. Note that in grammar, to decline a noun is to give its case forms, which is a third and unrelated job for the same word.
1verbdeclineTo politely say no to an offer.
“She politely declined his offer of a lift home.”
2verbworseTo fall or get worse.
“His health declined quickly after the operation.”
3nounworseningA fall or worsening.
“The decline was gradual and then very sudden.”
decline is a refusing or falling.
Latin declinare means to bend away — de- plus clinare, to lean, the same root as incline and recline. Declining an offer is leaning away from it, and a decline is a leaning downward.
Proto-Indo-European
*ḱley-
Middle English
declinen
English, today
decline
From Middle English declinen, and ultimately Latin declīnō (“to bend, turn aside, deflect, inflect, decline”), from Proto-Indo-European ḱley- (English lean). The senses arrived from two separate pathways in Middle English:
Etymology from Wiktionary, CC BY-SA
Practised in Ways of Speaking