A sidecheck is a piece of equipment for a horse. It goes from the bridle to the saddle to keep the horse from moving its head too much.
A sidecheck is a tool for making sure a horse behaves well while someone is riding it.
Examples:
The horse wears a sidecheck when it goes for a ride.
The sidecheck helps the rider control the horse.
The sidecheck is made of leather and metal.
The sidecheck is like a seatbelt for the horse.
The sidecheck is very important for keeping the horse safe.
The sidecheck is the horse's friend when it's time to ride.