Ask what a Gambeson is

"Dude," you say, "What the hell is a gambeson?"

"You know," mutterers the guard, "It's a... well, it's... Actually I've never really thought about it. I always assumed that it is some sort of blunt object."

"Well," you ejaculate, "don't just stand there in ignorance! Look it up!"

As the guard runs off to obtain a dictionary, you smile in satisfaction. You knew all along that a gambeson is a defensive garment formerly in use for the body, made of cloth stuffed and quilted. The joke is on the guard!

You escape from your cell before the guard returns.