Source : Webster's Revised Unabridged Dictionary (1913)

Octroi \Oc`troi"\, n. [F.]
   1. A privilege granted by the sovereign authority, as the
      exclusive right of trade granted to a guild or society; a
      concession.

   2. A tax levied in money or kind at the gate of a French city
      on articles brought within the walls. [Written also
      {octroy}.]

Source : WordNet®

octroi
     n : a tax on various goods brought into a town