A shunt is a small tube that goes inside the body to drain fluid. It also means to divert in a general way, like if you shunt the thought of tubes in your body, you think about rainbows and kittens instead.
Although shunt usually refers to a tube that drains blood or other fluid out of a part of the body, shunt also means to bypass. If a train is shunted, it’s diverted from the main track onto a side track. The word may have come from shun, as in “turn away,” which is what a shunt essentially does. It turns something away from where it was headed.