Wane

wane verb, waned, wan‧ing, noun

–verb (used without object)
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.

–noun
5.a gradual decrease or decline in strength, intensity, power, etc.
6.the drawing to a close of life, an era, a period, etc.
7.the waning of the moon.
8.a period of waning.
9.a defect in a plank or board characterized by bark or insufficient wood at a corner or along an edge, due to the curvature of the log.

—Idiom
10.on the wane, decreasing; diminishing: The popularity of that song is on the wane.
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[Origin: bef. 900; ME wanen (v.), OE wanian to lessen; c. MD, MHG wanen, ON vana to cause to wane, destroy]

—Synonyms 1, 2. diminish, fail, sink. 5. diminution; failure, decay.