Declension

Definition:

(n.) The act or the state of declining; declination; descent; slope.
(n.) A falling off towards a worse state; a downward tendency; deterioration; decay; as, the declension of virtue, of science, of a state, etc.
(n.) Act of courteously refusing; act of declining; a declinature; refusal; as, the declension of a nomination.
(n.) Inflection of nouns, adjectives, etc., according to the grammatical cases.
(n.) The form of the inflection of a word declined by cases; as, the first or the second declension of nouns, adjectives, etc.
(n.) Rehearsing a word as declined.

Compare declension with other words:

decimate vs. declension