The Collaborative International Dictionary of English v.0.48:

Turnpike \Turn"pike`\, n. [Turn + pike.]
   1. A frame consisting of two bars crossing each other at
      right angles and turning on a post or pin, to hinder the
      passage of beasts, but admitting a person to pass between
      the arms; a turnstile. See Turnstile, 1.
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            I move upon my axle like a turnpike.  --B. Jonson.
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   2. A gate or bar set across a road to stop carriages,
      animals, and sometimes people, till toll is paid for
      keeping the road in repair; a tollgate.
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   3. A turnpike road. --De Foe.
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   4. A winding stairway. [Scot.] --Sir W. Scott.
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   5. (Mil.) A beam filled with spikes to obstruct passage; a
      cheval-de-frise. [R.]
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   Turnpike man, a man who collects tolls at a turnpike.

   Turnpike road, a road on which turnpikes, or tollgates, are
      established by law, in order to collect from the users
      tolls to defray the cost of building, repairing, etc.
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The Collaborative International Dictionary of English v.0.48:

Turnpike \Turn"pike`\, v. t. [imp. & p. p. Turnpiked; p. pr. &
   vb. n. Turnpiking.]
   To form, as a road, in the manner of a turnpike road; to
   throw into a rounded form, as the path of a road. --Knowles.
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WordNet (r) 3.0 (2006):

turnpike
    n 1: (from 16th to 19th centuries) gates set across a road to
         prevent passage until a toll had been paid
    2: an expressway on which tolls are collected [syn: turnpike,
       toll road]