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1.
The act of pleasuring people of considerable age difference to yourself

e.g, I'm gonna go down to the bingo hall tonight and pick up some old ladies: take em for a bit of waning
by chaotica March 22, 2006
 
2.
If something's terrible or bad or boring or just generally negative, it's 'waning'. Derived from the cycles of the moon. Opposite of waxing
I hate having to eat brussel sprouts at xmas, they're waning!
by SpazOnTheHorizon January 06, 2012