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1.
An emoticon that resembles a penis, but has a three at the end. More potent and deadly than your garden-variety penis.
Hmm. That's quite a threenis.
by Raw Threenis May 06, 2009
 
2.
Three conjoined phalluses located in the pelvic cavity, directly above the the testes. Contrary to popular belief, there is no "factor tree", I.E. hydra rules do not apply.
Yo man, my bro johnny has the craziest threenis setup in his jeans. The ladies have to watch out for him.
by call of duty: black cocks July 20, 2011
 
3.
The nickname given to someone who performs three blow jobs on three different guys in the span of a weekend.
"Hey Threenis, how was your weekend?"
by J Bigs March 31, 2007