Source : Webster's Revised Unabridged Dictionary (1913)

Electrometer \E`lec*trom"e*ter\, n. [Electro- + -meter: cf. F.
   ['e]lectrom[`e]tre.] (Physics)
   An instrument for measuring the quantity or intensity of
   electricity; also, sometimes, and less properly, applied to
   an instrument which indicates the presence of electricity
   (usually called an electroscope).

   {Balance electrometer}. See under {Balance}.

Source : WordNet®

electrometer
     n : meter to measure electrostatic voltage differences; draws no
         current from the source