Tailboard and Tail gate

Tailboard noun - A gate at the rear of a vehicle; can be lowered for loading.

Tail gate and tailboard are semantically related. In some cases you can replace phrase "Tail gate" with "Tailboard", this terms are similar.

Tail gate noun - A gate downstream from a lock or canal that is used to control the flow of water at the lower end.

Tailboard and tail gate are semantically related. You can use "Tailboard" instead a noun phrase "Tail gate".