Other forms: oncomings
If you're standing on the tracks and a train is heading right for you, it's oncoming. Quick, jump out of the way!
You'll almost always find the adjective oncoming describing a vehicle or other large object that's moving fast in your direction, whether it's an oncoming car, oncoming traffic, or an oncoming skateboarder who doesn't see you standing there. Much less often, oncoming means "imminent" or "upcoming:" "The oncoming summer holidays were something to look forward to."