The Collaborative International Dictionary of English v.0.48:

Potentiometer \Po*ten`ti*om"e*ter\, n. [Potential + -meter.]
   (Elec.)
   An instrument for measuring or comparing electrial potentials
   or electro-motive forces.
   [1913 Webster]

WordNet (r) 3.0 (2006):

potentiometer
    n 1: a measuring instrument for measuring direct current
         electromotive forces
    2: a resistor with three terminals, the third being an
       adjustable center terminal; used to adjust voltages in radios
       and TV sets [syn: potentiometer, pot]