The Collaborative International Dictionary of English v.0.48:

Electro-motive \E*lec`tro-mo"tive\, a.
   Producing electro-motion; producing, or tending to produce,
   electricity or an electric current; causing electrical action
   or effects.
   [1913 Webster]

   Electro-motive force (Physics), the force which produces,
      or tends to produce, electricity, or an electric current;
      sometimes used to express the degree of electrification as
      equivalent to potential, or more properly difference of
      potential.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

E M F \E. M. F.\ (Physics)
   An abbreviation for electro-motive force.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

electromotive force
    n 1: the rate at which energy is drawn from a source that
         produces a flow of electricity in a circuit; expressed in
         volts [syn: voltage, electromotive force, emf]