1. noun, The wing or foil at the rear of a car providing downforce, often made with form rather than function
in mind, to adorn the rear of the cars driven around your town centre by mouth-breathers
who think they're in The Fast & the Furious
2. noun, A piece of information likely to ruin dramatic tension in any piece of entertainment if discovered too early. Usually any plot development revealed more than a third of the way through the story. She's a man, he's a ghost, it's his sledge, he's a clone, etc.
3. verb, To ruin any piece of entertainment by revealing such information.
4. verb, To protect others from entertainment being ruined by obscuring such information from them.