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.
      [1913 Webster]

            I move upon my axle like a turnpike.  --B. Jonson.
      [1913 Webster]

   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.
      [1913 Webster]

   3. A turnpike road. --De Foe.
      [1913 Webster]

   4. A winding stairway. [Scot.] --Sir W. Scott.
      [1913 Webster]

   5. (Mil.) A beam filled with spikes to obstruct passage; a
      cheval-de-frise. [R.]
      [1913 Webster]

   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.
      [1913 Webster]

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.
   [1913 Webster]

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]

Moby Thesaurus II by Grady Ward, 1.0:

108 Moby Thesaurus words for "turnpike":
   Autobahn, French door, US highway, alley, alleyway, archway,
   arterial, arterial highway, arterial street, artery, autoroute,
   autostrada, avenue, back door, barway, belt highway, blind alley,
   boulevard, bulkhead, bypass, byway, camino real, carriage entrance,
   carriageway, causeway, causey, cellar door, cellarway, chaussee,
   circumferential, close, corduroy road, county road, court,
   crescent, cul-de-sac, dead-end street, dike, dirt road, door,
   doorjamb, doorpost, doorway, drive, driveway, expressway, freeway,
   front door, gate, gatepost, gateway, gravel road, hatch, hatchway,
   highroad, highway, highways and byways, interstate highway, lane,
   lintel, local road, main drag, main road, mews, motorway, parkway,
   pave, paved road, pike, place, plank road, porch, portal,
   porte cochere, postern, primary highway, private road, propylaeum,
   pylon, right-of-way, ring road, road, roadbed, roadway,
   route nationale, row, royal road, scuttle, secondary road,
   side door, speedway, state highway, stile, storm door, street,
   superhighway, terrace, thoroughfare, threshold, through street,
   thruway, toll road, tollgate, township road, trap, trap door,
   turnstile, wynd



Bouvier's Law Dictionary, Revised 6th Ed (1856):

TURNPIKE. A public road paved with stones or other hard substance.
     2. Turnpike roads are usually made by corporations to which a power to
make them has been granted. The grant of such power passes not only an
easement for the road itself, but also so much land as is connected with it;
as, for instance, for a toll house and a cellar under it, and a well for the
use of the family. 9 Pick. R. 109. A turnpike is a public highway, and a
building erected before the turnpike was made, though upon a part out of the
travelled path, if continued there is a nuisance. 16 Pick. R. 175. Vide
Road; Street; Way.