Definition from Wiktionary, the free dictionary
westering (not comparable)
- (especially of heavenly bodies, particularly the sun) Moving westward, near the west.
1927, H. P. Lovecraft, The Very Old Folk:
- The hills rose scarlet and gold to the north of the little town, and the westering sun shone ruddily and mystically on the crude new stone and plaster buildings of the dusty forum and the wooden walls of the circus some distance to the east.