The Collaborative International Dictionary of English v.0.48:

Tourniquet \Tour"ni*quet\, n. [F., fr. tourner to turn.] (Surg.)
   An instrument for arresting hemorrhage. It consists
   essentially of a pad or compress upon which pressure is made
   by a band which is tightened by a screw or other means.
   [1913 Webster]

WordNet (r) 3.0 (2006):

tourniquet
    n 1: bandage that stops the flow of blood from an artery by
         applying pressure [syn: compression bandage,
         tourniquet]