antitorque rotor

[an-tee-tawrk, an-tahy-]
noun Aeronautics.
  1. (on certain helicopters) a small rotor on the tail, turning in the vertical plane and providing a thrust whose torque opposes and compensates for the torque of the main rotor.

Origin of antitorque rotor Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018