wane
/ˈwān/
verb
to decrease in size, extent, or degree : dwindle: such as
to diminish in phase or intensity —used chiefly of the moon, other satellites, and inferior planets
to become less brilliant or powerful : dim
noun
the act or process of waning
a period or time of waning; specifically : the period from the full moon to the new moon
a defect in lumber characterized by bark or a lack of wood at a corner or edge
strength on the wane
idiom
becoming smaller or less
Her popularity was on the wane.