the state of a penis which is not altogether flaccid nor erect. It will often occur at inopportune embarrasing times and will be brought on purposefully by a cunning sexy woman pretending she has no idea what she is doing.
"why are you still friends with some of your ex-boyfriends?"

"I like to keep them healthy and providing the regular semi keeps the circulatory system in check."
by MintyLeila June 18, 2005
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the in-between state of a limp dick and a usable hard-on. can be on the way to hard, on the way back from hard, or never allowed to get more than 60% (+/-) hard.
many a young man learn to hide their semi with text books after day-dreaming in class
by the mac al February 28, 2006
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A person who has a high tolerance, or can take numerous shots, blows, etc, but remains stoic or unfazed. The usual context is referring to a person in a fight or a person drinking numerous shots.
He's not even fazed. We got ourselves a full-blown semi.
by The Great Dark January 31, 2015
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The word that comes up on t9 phones when the word "penis" is intended to be typed.
I got a text from Benjy that says, "I put my semis in her butt."
by Danielwritesstuff January 14, 2009
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A small boner over something none sexually related. It will be about 50% smaller
100% on a maths test forced him to get a semi
by Ben Ski Don May 03, 2010
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1 -(n.) Any semi-automatic weapon; semi-shots, smg's, etc. (pronounced "seh-MEE")

2 -(n.) An 18-wheeler truck (pronounced "seh-MI")

1 - "Semi's are only half as fun as automatics."

2 - "Aparrently a semi loaded with cocaine and doritos rolled over on the freeway yesterday.
by Lil Dre March 19, 2006
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