Definition of wanes:
(v) :
(intransitive) To progressively lose its splendor, value, ardor, power, intensity etc.; to decline.
(v) :
(intransitive) For light to dim or diminish in strength.
(v) :
(intransitive, astronomy) For the Moon to pass through the phases of its monthly cycle where its surface is less and less visible.
(n) :
A gradual diminution in power, value, intensity etc.
(n) :
The lunar phase during which the sun seems to illuminate less of the moon as its sunlit area becomes progressively smaller as visible from Earth.
(n) :
(literary) The end of a period.