undea Posted in U Best definition undea n. an idea that is disastrously bad; the antithesis of a good idea. “Dude, I’ve come up with a scheme where we could steal and ATM and put it in our dorm room.” “That is an undea.” How satisfied are you with the definition? Looking for undea meaning? Delighted that you discovered the greatest determine on our web site! Recently this definition was actually observed 35 times.