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2.
When you have half of a boner. Kind of like a chub. You cannot control it. It is just there. Big and thick.
Guy 1: "WTF?!?! do you have a boner?"
Guy 2: "Nah dude, im just half masting"
Guy 1: "ohh"
by My turbin is dirty February 17, 2012
 
1.
when your pooping and realize your out of t.p. and have to waddle with your pants around your ankles or knees to go to the hallway closet to get more toilet paper.
my mom spotted me half masting and damn it was embarrasing
by vloky July 01, 2004