De*clen"sion (?), n. [Apparently corrupted fr. F. d'eclinaison, fr. L. declinatio, fr. declinare. See Decline, and cf. Declination.]
1.
The act or the state of declining; declination; descent; slope.
The declension of the land from that place to the sea.
T. Burnet.
2.
A falling off towards a worse state; a downward tendency; deterioration; decay; as, the declension of virtue, of science, of a state, etc.
Seduced the pitch and height of all his thoughts
To base declension.
Shak.
3.
Act of courteously refusing; act of declining; a declinature; refusal; as, the declension of a nomination.
4. Gram. (a)
Inflection of nouns, adjectives, etc., according to the grammatical cases.
(b)
The form of the inflection of a word declined by cases; as, the first or the second declension of nouns, adjectives, etc.
(c)
Rehearsing a word as declined.
⇒ The nominative was held to be the primary and original form, and was likened to a perpendicular line; the variations, or oblique cases, were regarded as fallings (hence called casus, cases, or fallings) from the nominative or perpendicular; and an enumerating of the various forms, being a sort of progressive descent from the noun's upright form, was called a declension.
Harris.
Declension of the needle, declination of the needle.
© Webster 1913.