[1] : The Collaborative International Dictionary of English v.0.48

tandem \tan"dem\, n.
   1. a team of horses harnessed one before the other. "he drove
      tandems." --thackeray.
      1913 webster

   2. a tandem bicycle or other vehicle.
      webster 1913 suppl.

   tandem bicycle or tandem tricycle, one for two persons in
      which one rider sits before the other.
      1913 webster
see also:
tandem bicycle tandem tricycle 

[2] : WordNet (r) 2.0

tandem bicycle
     n : a bicycle with two sets of pedals and two seats syn: bicycle-built-for-two,
          tandem
see also:
bicycle-built-for-two tandem 

Tandem >> T Words
Tandem, definition of term: Tandem
tandem_pag1.html

Bicycle >> B Words
Bicycle, definition of term: Bicycle
bicycle_pag1.html