Rails and Spline

Rails noun - A bar or pair of parallel bars of rolled steel making the railway along which railroad cars or other vehicles can roll.

Spline and rails are semantically related. In some cases you can use "Spline" instead a noun "Rails".

Spline noun - A thin strip (wood or metal).

Rails and spline are semantically related. Sometimes you can replace term "Rails" with "Spline", this nouns are similar.