Colloquially it is a synonym, but technically the "Sin of Onan" for which it is named for is actually an instance of coitus interruptus.
"Onanism -- it's a hands-on job"

by Jay Jay Ron March 20, 2008
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from New Latin onanismus, from Onan, son of Judah (Gen 38:9),
masturbation, coitus interruptus, self-gratification.
Jon can'g get any, so he practices onanism.
by El Cid June 21, 2003
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I think someone did onanism in my coffee again. That sure aint milk.

Well you would know scab mouth!
by Anonymous September 17, 2003
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The withdrawl method of birth control

(removeing ones penis before reaching orgasm)

-not an effective method of birth control
Lets do onanism tonight hunny
by dude August 24, 2003
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Stands for One Network America News network. Sometimes mistakenly referred to OAN, ONAN is a small-time, mom's basement "news" operation. Shows are typically hosted by distended colons and strung-out gap-toothed cam girls. Owned by Gil "Red" Herring, their only real claim to fame is the manufacture and marketing of matching sets of presidential knee pads and butt snorkels.
"Did you see that 'reporter' from ONAN at the federal conronavirus briefing? What do you think will happen first--she finally gets her adult teeth, or she promotes out of fifth grade this year?"
by ToddUncommon April 07, 2020
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to wank,
to tame the one eyed monster,
to make the cyclops cry,
man's favourite outlet,
a date with mrs palm and her five
lovely daugters,
toss yourself off,
etc etc
"now on the subject of onanism...we dont want to find you hunched double on the sofa bed pumping your fist" (league of gentlemen)
by pinkpill December 01, 2004
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Short-hand for "on another note"
Grace: are u going to Chad's party on Friday?

Ben: nah too many frat boys. onan do u wanna go Chilli's on Sat?
by ittybittysmalls September 11, 2019
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