Crushkiller is a term used by Rysn to describe her babsk, Vstim, in his arguing and haggling with Thresh-son-Esan over the value of his own metal scraps versus the chickens of Thresh.[1]

Each eventually devalued his wares as worthless, yet came to an agreement on a deal, though Rysn couldn't grasp just how they came to it.[1]

A Crushkiller most likely refers to some sort of creature on Roshar.