Source : Webster's Revised Unabridged Dictionary (1913)

Tandem engine \Tandem engine\
   A steam engine having two or more steam cylinders in line,
   with a common piston rod.

Tandem \Tan"dem\, n.
   A team of horses harnessed one before the other. ``He drove
   tandems.'' --Thackeray.

   {Tandem engine}, a compound steam engine having two or more
      steam cylinders in the same axis, close to one another.

   {Tandem bicycle} or {tricycle}, one for two persons in which
      one rider sits before the other.