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1.
A regular bowel movement that is propelled out of your rectum by a large pocket of gas behind the bowel movement.
All those Taco Bell tacos gave me a huge benignus.
by Cancer Killer February 02, 2010
 
2.
When you have to deficate, and you can't for awhile, until it is blown out by gas stored up behind it. Usually ends up splashing you from the forceful entry into the toilet.
I sat on the can for at least a half hour, then I had a benignus, and it was all over.
by MannySheen April 28, 2005