1 decrease, diminish, grow less, lessen, decline, die out, abate, ebb, subside, fade (away), dim, taper off, peter out, wind down, weaken:
The waning moon cast its pale light on the dying knight. As his strength waned he could no longer lift his sword.
2 draw to a close, end, terminate:
The day waned into a gloomy evening.
3 decrease, diminution, lessening, decline, abatement, ebb, subsidence, fading, tapering off, petering out, winding down, weakening, deterioration, degeneration:
The 1970s saw the wane in popularity of large, gas-guzzling cars.
4 on the wane. on the decrease or decline or ebb, diminishing, decreasing, declining, abating, subsiding, fading, tapering off, petering out, winding down, weakening, deteriorating, degenerating:
The economy is recovering, and inflation is on the wane. Since that latest illness, my energy has been on the wane.