The Collaborative International Dictionary of English v.0.48:

Ohm \Ohm\ ([=o]m), n. [So called from the German electrician, G.
   S. Ohm.] (Elec.)
   The standard unit in the measure of electrical resistance,
   being the resistance of a circuit in which a potential
   difference of one volt produces a current of one amp['e]re.
   As defined by the International Electrical Congress in 1893,
   and by United States Statute, it is a resistance
   substantially equal to 10^9 units of resistance of the C.
   G. S. system of electro-magnetic units, and is represented by
   the resistance offered to an unvarying electric current by a
   column of mercury at the temperature of melting ice 14.4521
   grams in mass, of a constant cross-sectional area, and of the
   length of 106.3 centimeters. As thus defined it is called the
   international ohm.
   [1913 Webster]

   Ohm's law (Elec.), the statement of the fact that the
      strength or intensity of an electrical current is directly
      proportional to the electro-motive force, and inversely
      proportional to the resistance of the circuit.
      [1913 Webster]