The Collaborative International Dictionary of English v.0.48:

Conestoga wagon \Con`es*to"ga wag`on\ or Conestoga wain
\Con`es*to"ga wain\ [From Conestoga, Pennsylvania.]
   A kind of large broad-wheeled wagon, usually covered, for
   traveling in soft soil and on prairies.
   [Webster 1913 Suppl.]