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1.
1. An apathetic boner.
2. It's hanging in there.
3. The point right before a full blown hard-on.
That chick gave me a raging semi.
by Assadi and Brun June 07, 2007
 
2.
A chub, or partially erect penis, that just won't quit. It is often on the verge of being painful and can happen at random times like at job interviews or when taking the SATs. Unfortunately, it's hard enough to be noticeable, but not hard enough to belt-tuck.
I was in the middle of the test and I got hit with this crazy raging semi.
by Barcak March 05, 2007