A homemade weapon usually made out of old crap lying around like broken glass or metal. A shank usually is only for stabbing and has no cutting edge (like a dart, but a lot bigger and more dangerous).
As a verb shank means to stab somebody to death with a shank, with quick short motions to the area just below the ribs.
-In both of these senses shiv
means the same thing.
"Shank" can also be used in golf to describe a terrible slice or duff resultant from the club head not centered on the ball during the swing. Also a verb.
I've also heard from a guy in NC that they use "shank" to mean pantsing
where he lives. Nobody else I've asked says this is true, though. Usually they yell "shank" as they pull down the pants.