declension

What it means

1. countableuncountableA falling off, decay or descent.

   The custom of rolling a burning wheel down a hill […] might well pass for an imitation of the sun's course in the sky, and the imitation would be especially appropriate on Midsummer Day when the sun's annual declension begins.

   1890, James George Frazer, The Golden Bough, volume 2, page 268

   1 more example

   Refinement of feeling, intellectual tastes, and a noble hospitality, were among the features of his character; and hoary years brought no mental declension, and drew no shade over the ardent affections by which he was distinguished, and in whose reciprocity, was his undeclining solace.

   1845, Lydia Sigourney, Scenes in my Native Land, The Great Oak of Geneseo, page 86

2. countableuncountablegrammarThe act of declining a word; the act of listing the inflections of a noun, pronoun or adjective in order.
3. countableuncountablegrammarThe product of that act; a list of declined forms.

   a page full of declensions

In a sentence

Refinement of feeling, intellectual tastes, and a noble hospitality, were among the features of his character; and hoary years brought no mental declension, and drew no shade over the ardent affections by which he was distinguished, and in whose reciprocity, was his undeclining solace.

1845, Lydia Sigourney, Scenes in my Native Land, The Great Oak of Geneseo, page 86

Where it comes from

1. Latindēclīnātiō
2. Middle Frenchdeclinaison
3. Middle Englishdeclinson
4. Englishdeclension

From late Middle English declinson, from Middle French declinaison (Modern French: déclinaison), from Latin dēclīnātiō. Doublet of declination.