no obj.
1- (of the moon) have a progressively smaller part of its visible surface illuminated, so that it appears to decrease in size（月亮）亏缺。
1.1
- (especially of a condition or feeling) decrease in vigour, power, or extent; become weaker（尤指状况、感觉）衰落, 减少, 减弱：
confidence in the dollar waned.
对美元的信心减弱了。
短语
on the wane
- becoming weaker, less vigorous, or less extensive正在减弱, 正在衰弱, 正在减少：
the epidemic was on the wane.
该流行病正在减退。
词源
Old English wanian 'lessen'， of Germanic origin; related to Latin vanus 'vain'.