Source : Webster's Revised Unabridged Dictionary (1913)

Doubler \Dou"bler\, n.
   1. A part of a distilling apparatus for intercepting the
      heavier fractions and returning them to be redistilled.

   2. (Calico Printing) A blanket or felt placed between the
      fabric and the printing table or cylinder.

Doubler \Dou"bler\, n.
   1. One who, or that which, doubles.

   2. (Elec.) An instrument for augmenting a very small quantity
      of electricity, so as to render it manifest by sparks or
      the electroscope.

Source : WordNet®

doubler
     n : an electronic device that doubles the voltage or the
         frequency of an input signal