this expression is a superstition that is used in the hope that a good thing will continue to occur even after its mentioned.
For Example : "My throat is finally feeling better, knock on wood!"

or

"I'm so happy it hasn't rained yet, knock on wood"
by [DEE]best! December 24, 2009
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1. A phrase used to express that something will or will not happen. This expression alludes to the ages-old superstition that literally knocking on wood would ward off evil spirits.
2. To masturbate, said of males.
(made-up scene from GTA San Andreas)

(at the beach)

Kent Paul: (ogling a hot girl come out of the water) Oi Maccer, just take a look at what just breezed out of the blue. That height, that arse, those jugs, those curves! Blimey if I'd be given the chance now I'd get to chuck my junk in that, knock on wood!
Maccer: Indeed man! Knock on wood, eh. Well alright then! *starts masturbating*
Kent Paul: No, jack-off Jimmy, not... ohh, *mumbles* fucking Northeners!

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Mark H. Proud Urban Dictionary slang author since February 2004.
by Mark H September 30, 2005
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A few light tapping motions dat an able-to-ovulate chick makes on her sexual partner's "woody" wif her knuckles prior to his entering her, in da superstitious hope dat said action will bring her good luck --- i.e., dat said impending bodily-union won't get her "knocked up".
Practicing da rhythm method or taking birth-control pills are indeed often-effective ways to lessen da risk of unwanted pregnancy, but they are by no means reliable, so you'd likely still feel da urge to "knock on wood" each time you "do it" without a condom.
by QuacksO February 27, 2023
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yet another term that is sexual innuendo for masturbation.
This chick is hot. I gotta knock on wood really quick.
by notorious B.A.M. February 4, 2010
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to take one's hand (which is in the shape of a fist..) and bang it on a dead tree.
crogi: "ouch! i hurt my hand knocking on that wood. it looks like i'm bleeding"
bob: "want a cool glow in the dark harry potter band aid??"
crogi: "SA-WEET!"
by kazoomafoo June 8, 2005
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to take one's hand (which is in the shape of a fist..) and bang it on a dead tree.
in karate we like to knock on wood!
by kazoomafoo May 30, 2005
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