"Declension" is a word in ENGLISH

Rehearsing a word as declined.

The form of the inflection of a word declined by cases;
as, the first or the second declension of nouns, adjectives, etc.

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

Act of courteously refusing; act of declining; a
declinature; refusal; as, the declension of a nomination.

The act or the state of declining; declination;
descent; slope.

Inflection of nouns, adjectives, etc., according to the
grammatical cases.