Rotor and Tail rotor

Rotor noun - Rotating mechanism consisting of an assembly of rotating airfoils.

Tail rotor and rotor are semantically related. In some cases you can replace phrase "Tail rotor" with "Rotor", this terms are similar.

Tail rotor noun - Rotor consisting of a rotating airfoil on the tail of a single-rotor helicopter; keeps the helicopter from spinning in the direction opposite to the rotation of the main rotor.

Rotor and tail rotor are semantically related. You can use "Rotor" instead a noun phrase "Tail rotor".