*declension*

n. [ Apparently corrupted fr. F. déclinaison, fr. L. declinatio, fr. declinare. See Decline, and cf. Declination. ] 1. The act or the state of declining; declination; descent; slope. [ 1913 Webster ]

The declension of the land from that place to the sea. T. Burnet. [ 1913 Webster ]

2. A falling off towards a worse state; a downward tendency; deterioration; decay; as, the declension of virtue, of science, of a state, etc. [ 1913 Webster ]

Seduced the pitch and height of all his thoughts
To base declension. Shak. [ 1913 Webster ]

3. Act of courteously refusing; act of declining; a declinature; refusal; as, the declension of a nomination. [ 1913 Webster ]

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. [ 1913 Webster ]

☞ 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. [ 1913 Webster ]

Declension of the needle, declination of the needle. [ 1913 Webster ]