Webster's Revised Unabridged Dictionary · 1913

Decline

Decline , intransitive verb

[Old English declinen to bend down, lower, sink, decline (a noun), French décliner to decline, refuse, from Latin declinare to turn aside, inflect (a part of speech), avoid; de- + clinare to incline; akin to English lean. See Lean, v. i.]

1.
To bend, or lean downward; to take a downward direction; to bend over or hang down, as from weakness, weariness, despondency, etc.; to condescend.
With declining head. — Shakespeare
He... would decline even to the lowest of his family. — Lady Hutchinson
Disdaining to decline, Slowly he falls, amidst triumphant cries. — Byron
The ground at length became broken and declined rapidly. — Sir W. Scott
2.
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.
That empire must decline Whose chief support and sinews are of coin. — Waller
And presume to know... Who thrives, and who declines. — Shakespeare
3.
To turn or bend aside; to deviate; to stray; to withdraw; as, a line that declines from straightness; conduct that declines from sound morals.
Yet do I not decline from thy testimonies. — Bible (KJV) - Psalm cxix. 157
4.
To turn away; to shun; to refuse; -- the opposite of accept or consent; as, he declined, upon principle.

Decline , transitive verb

1.
To bend downward; to bring down; to depress; to cause to bend, or fall.
In melancholy deep, with head declined. — Thomson
And now fair Phoebus gan decline in haste His weary wagon to the western vale. — Spenser
2.
To cause to decrease or diminish. [Obsolete]
You have declined his means. — Beau. & Fl
He knoweth his error, but will not seek to decline it. — Burton
3.
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.
Could I Decline this dreadful hour? — Massinger
4.
(Grammar) To inflect, or rehearse in order the changes of grammatical form of; as, to decline a noun or an adjective.
After the first declining of a noun and a verb. — Ascham

Now restricted to such words as have case inflections; but formerly it was applied both to declension and conjugation.

5.
To run through from first to last; to repeat like a schoolboy declining a noun. [Rare] — Shakespeare

Decline , noun

[French déclin. See Decline, v. i.]

1.
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.
Their fathers lived in the decline of literature. — Swift
2.
(Medicine) That period of a disorder or paroxysm when the symptoms begin to abate in violence; as, the decline of a fever.
3.
A gradual sinking and wasting away of the physical faculties; any wasting disease, esp. pulmonary consumption; as, to die of a decline. — Dunglison