The Collaborative International Dictionary of English v.0.48:

Dynamometer \Dy`na*mom"e*ter\, n. [Cf. F. dynamom[`e]tre. See
   Dynameter.]
   An apparatus for measuring force or power; especially,
   muscular effort of men or animals, or the power developed by
   a motor, or that required to operate machinery.
   [1913 Webster]

   Note: It usually embodies a spring to be compressed or weight
         to be sustained by the force applied, combined with an
         index, or automatic recorder, to show the work
         performed. Dynamometric

WordNet (r) 3.0 (2006):

dynamometer
    n 1: measuring instrument designed to measure power [syn:
         dynamometer, ergometer]