pilot balloon
    n 1: meteorological balloon used to observe air currents

Pilot \Pi"lot\, n. [F. pilote, prob. from D. peillood plummet,
   sounding lead; peilen, pegelen, to sound, measure (fr. D. &
   G. peil, pegel, a sort of measure, water mark) + lood lead,
   akin to E. lead. The pilot, then, is the lead man, i. e., he
   who throws the lead. See Pail, and Lead a metal.]
   1. (Naut.) One employed to steer a vessel; a helmsman; a
      steersman. --Dryden.
      [1913 Webster]

   2. Specifically, a person duly qualified, and licensed by
      authority, to conduct vessels into and out of a port, or
      in certain waters, for a fixed rate of fees.
      [1913 Webster]

   3. Figuratively: A guide; a director of another through a
      difficult or unknown course.
      [1913 Webster]

   4. An instrument for detecting the compass error.
      [1913 Webster]

   5. The cowcatcher of a locomotive. [U.S.]
      [1913 Webster]

   6. (A["e]ronautics) One who flies, or is qualified to fly, an
      airplane, balloon, or other flying machine.
      [Webster 1913 Suppl. +PJC]

   7. (Mach.) A short plug at the end of a counterbore to guide
      the tool. Pilots are sometimes made interchangeable.
      [Webster 1913 Suppl.]

   8. (Mining) The heading or excavation of relatively small
      dimensions, first made in the driving of a larger tunnel.
      [Webster 1913 Suppl.]

   9. (Television) a filmed or taped episode of a proposed
      television series, produced as an example of the series.
      It may be shown only to those television broadcast
      executives who may decide whether to buy the rights to the
      series, or aired to test viewer reaction or to interest
      sponsors. Also called pilot film or pilot tape.
      [PJC]

   Pilot balloon, a small balloon sent up in advance of a
      large one, to show the direction and force of the wind.

   Pilot bird. (Zool.)
      (a) A bird found near the Caribbee Islands; -- so called
          because its presence indicates to mariners their
          approach to these islands. --Crabb.
      (b) The black-bellied plover. [Local, U.S.]

   Pilot boat, a strong, fast-sailing boat used to carry and
      receive pilots as they board and leave vessels.

   Pilot bread, ship biscuit.

   Pilot cloth, a coarse, stout kind of cloth for overcoats.
      

   Pilot engine, a locomotive going in advance of a train to
      make sure that the way is clear.

   Pilot fish. (Zool)
      (a) A pelagic carangoid fish (Naucrates ductor); -- so
          named because it is often seen in company with a
          shark, swimming near a ship, on account of which
          sailors imagine that it acts as a pilot to the shark.
      (b) The rudder fish (Seriola zonata).

   Pilot jack, a flag or signal hoisted by a vessel for a
      pilot.

   Pilot jacket, a pea jacket.

   Pilot nut (Bridge Building), a conical nut applied
      temporarily to the threaded end of a pin, to protect the
      thread and guide the pin when it is driven into a hole.
      --Waddell.

   Pilot snake (Zool.)
      (a) A large North American snake (Coluber obsoleus). It
          is lustrous black, with white edges to some of the
          scales. Called also mountain black snake.
      (b) The pine snake.

   Pilot whale. (Zool.) Same as Blackfish, 1.
      [1913 Webster]

Pilot balloon \Pilot balloon\
   A small, unmanned balloon sent up to indicate the direction
   of air currents.
   [Webster 1913 Suppl.]