The Collaborative International Dictionary of English v.0.48:

Ergometer \Er*gom"e*ter\, n. [Gr. ? work + -meter.] (Physics)
   A device for measuring, or an instrument for indicating,
   energy expended or work done; a dynamometer. --
   Er`go*met"ric, a.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

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