The Collaborative International Dictionary of English v.0.48:

isometric exercise \i`so*met"ric ex"er*cise\, n.
   A system of exercise to strengthen specific muscles of the
   body by pushing parts of the body (such as the two hands)
   strongly against each other, or against a fixed object, so
   that the muscles are strongly stressed, but are stretched
   only a little. It is claimed to produce strength in the
   muscles thus exercised. Also called isometrics.
   [PJC]

The Collaborative International Dictionary of English v.0.48:

isometrics \i`so*met"rics\, n.
   Same as isometric exercise.
   [PJC]

WordNet (r) 3.0 (2006):

isometrics
    n 1: muscle-building exercises (or a system of musclebuilding
         exercises) involving muscular contractions against
         resistance without movement (the muscles contracts but the
         length of the muscle does not change) [syn: isometrics,
         isometric exercise]