In music, the Italian term morendo means "fading or dying away". This fairly transparently comes from morior. But morior to me suggests the moment of death, rather than a gradual decline, and is also a fairly morbid word.
If I wanted an adjective (or participle) for "fading away" or "in decline", are there better alternatives to moriēns? I'm interested in both Greek and Latin.
ETA: Example sentences:
The Roman empire was in decline for a significant period before its actual fall.
We sat by the ocean at dusk, watching the sunlight fading away.
He would have preferred a quick death rather than fading away like this.