Same word as wane:

abate, atrophy, decline, decrease, die away, die down, die out, dim, draw to a close, drop, dwindle, ease off, ebb, fade, fade away, fail, fall, fall short, let up, moderate, peter out, relent, shrink, sink, slack off, slacken, subside, taper off, waste away, weaken, wind down, wither