Decline v. i. : To bend, or lean downward; to take a downward direction; to bend over or hang down, as from weakness, weariness, despondency, etc.; to condescend.

Decline v. i. : To tend or draw towards a close, decay, or extinction; to tend to a less perfect state; to become diminished or impaired; to fail; to sink; to diminish; to lessen; as, the day declines; virtue declines; religion declines; business declines.

Decline v. i. : To turn or bend aside; to deviate; to stray; to withdraw; as, a line that declines from straightness; conduct that declines from sound morals.

Decline v. i. : To turn away; to shun; to refuse; -- the opposite of accept or consent; as, he declined, upon principle.

Decline v. t. : To bend downward; to bring down; to depress; to cause to bend, or fall.

Decline v. t. : To cause to decrease or diminish.

Decline v. t. : To put or turn aside; to turn off or away from; to refuse to undertake or comply with; reject; to shun; to avoid; as, to decline an offer; to decline a contest; he declined any participation with them.

Decline v. t. : To inflect, or rehearse in order the changes of grammatical form of; as, to decline a noun or an adjective.

Decline v. t. : To run through from first to last; to repeat like a schoolboy declining a noun.

Decline v. i. : A falling off; a tendency to a worse state; diminution or decay; deterioration; also, the period when a thing is tending toward extinction or a less perfect state; as, the decline of life; the decline of strength; the decline of virtue and religion.

Decline v. i. : That period of a disorder or paroxysm when the symptoms begin to abate in violence; as, the decline of a fever.

Decline v. i. : A gradual sinking and wasting away of the physical faculties; any wasting disease, esp. pulmonary consumption; as, to die of a decline.

Example:
How and when to Decline a selling party invitation?

Taxonomy
Decline, free encyclopedia, organizational environment, law, Social decline, moral decline, moral behavior, Decline of the Roman Empire, search, free dictionary, over time, rational, non-rational, decision-making, abiding, behavior, iniquitous, outdating.

Defination from the web:
Decline is a change over time from previously efficient to inefficient organizational functioning, from previously rational to non-rational ... Decline refers to the degenerating of something whereas obsolete refers to the outdating of something or that it is no longer in use ...