Source : Webster's Revised Unabridged Dictionary (1913)

Oscillograph \Os"cil*lo*graph\, n. [L. oscillare to swing +
   -graph.] (Elec.)
   An apparatus for recording or indicating alternating-current
   wave forms or other electrical oscillations, usually
   consisting of a galvanometer with strong field, in which the
   mass of the moving part is very small and frequency of
   vibration very high. -- {Os`cil*lo*graph"ic}, a.

Source : WordNet®

oscillograph
     n : a device for making a record of the wave forms of
         fluctuating voltages or currents