wane

verb (used without object), waned, wan·ing.

1. to decrease in strength, intensity, etc.: Daylight waned, and night came on. Her enthusiasm for the cause is waning.
2. to decline in power, importance, prosperity, etc.: Colonialism began to wane after World War II.
3. to draw to a close; approach an end: Summer is waning.
4. (of the moon) to decrease periodically in the extent of its illuminated portion after the full moon.Compare wax²(def 2).