See shank for root definition.
Verb: to lift up your leg or ass cheek and deliver a rousing fart at the exact same time as a loud noise, to avoid being heard, much like the lead character in The Shawshank Redemption hit the pipe with the stone during the storm.
I was at my girlfriend's house watching a movie with her parents, and I really needed to shank one, so I waited until an explosion and shawshanked it perfectly. They never heard a thing so no one knew where the smell came from.
Verb: to lift one leg or ass cheek and deliver a rousing fart.
Noun: the result of lifting one leg or ass cheek to deliver a rousing fart.
Verb: Dude, I was sitting in one of those old wooden chairs when I shanked one so loud people heard it down the hall.
Noun: Dude, was that your shank I heard down the hall? It echoed all the way to our room.