Slang word for penis.
"Be right back, I'm gonna go drain the main vein".

"I drilled her with my main vein".
by mickyxtee May 9, 2009
Get the main vein mug.
The largest vein in the penis. Once the penis has become erect, the blue/purple vein becomes clearly visible.
"Seeing that chick naked got me so hard that my main vein was just bulging!!"
by PMchoisi June 8, 2009
Get the Main Vein mug.
The large vein that travels the length of a cock. Instrumental in delivering blood from the central artery during erection.
My cock was so hard, my main vein was swollen with blood.

I saw my heart beat as the main vein of my cock pulsated with blood.
by Tony from the Lido September 21, 2011
Get the Main Vein mug.
To snort a line of cocaine off of a fully erect penis
Me: Yo, do you even rail the main vein?
12 year old on Xbox live: Yeah, fucker, I rail the main vein every day!
by Blawkz February 9, 2015
Get the Rail the Main Vein mug.