Wane
noun
A gradual diminution in power, value, intensity etc.
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.
The end of a period.
verb
To progressively lose its splendor, value, ardor, power, intensity etc.; to decline.
Said of light that dims or diminishes in strength.
Said of the Moon as it passes through the phases of its monthly cycle where its surface is less and less visible.