Meaning of antitorque rotor

an•ti•torque' ro"tor

Pronunciation: (an"tē-tôrk', an"tī-), [key]
— Aeron. Aeron.
  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.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.