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1.
The state of being stuck between two points of view, understanding both but not favouring one over the other.
Seeing the relative merits of both Aerosmith and the White Stripes, John was the understandwich in what he considered an unnecessary argument.
by wordguy2 April 18, 2010
 
2.
1. (noun) snack-sized bits of understanding, the consumption of which would be similar to eating a sandwich, but in your mind

Popularized by the infamous rapper AK-47 in his as-yet untitled hit single from his breakthrough album "Down By the River" (Whimsy's Whack Records, 2009)
"Chew on those understandwiches, sucka!"
by yellow magnetic star March 31, 2010
 
3.
When two people have fought over involvement with a third party, they settle their dispute by having sexual relations with that person at the same time.
After Chad and Shane found out they were both dating Casey, they made up for it by making her the meat in their understandwich.
by Andherson November 02, 2013