The origin of the term is contested, but may be derived from “George Stick”, named for a possible inventor.
I knew the device itself predated gaming, but I always assumed it gained the joystick name from some game company. I’m surprised to to learn its unrelated!
I always assumed it was “joy” because games are fun, And it’s a stick design for playing video games so Joy. Stick. Joystick. But I’ve apparently assumed wrongly.