Source : Webster's Revised Unabridged Dictionary (1913)

Level \Lev"el\ (l[e^]v"[e^]l), n. [OE. level, livel, OF. livel,
   F. niveau, fr. L. libella level, water level, a plumb level,
   dim. of libra pound, measure for liquids, balance, water
   poise, level. Cf. {Librate}, {Libella}.]
   1. A line or surface to which, at every point, a vertical or
      plumb line is perpendicular; a line or surface which is
      everywhere parallel to the surface of still water; -- this
      is the true level, and is a curve or surface in which all
      points are equally distant from the center of the earth,
      or rather would be so if the earth were an exact sphere.

   2. A horizontal line or plane; that is, a straight line or a
      plane which is tangent to a true level at a given point
      and hence parallel to the horizon at that point; -- this
      is the apparent level at the given point.

   3. An approximately horizontal line or surface at a certain
      degree of altitude, or distance from the center of the
      earth; as, to climb from the level of the coast to the
      level of the plateau and then descend to the level of the
      valley or of the sea.

            After draining of the level in Northamptonshire.
                                                  --Sir M. Hale.

            Shot from the deadly level of a gun.  --Shak.

   4. Hence, figuratively, a certain position, rank, standard,
      degree, quality, character, etc., conceived of as in one
      of several planes of different elevation.

            Providence, for the most part, sets us on a level.
                                                  --Addison.

            Somebody there of his own level.      --Swift.

            Be the fair level of thy actions laid As temperance
            wills and prudence may persuade.      --Prior.

   5. A uniform or average height; a normal plane or altitude; a
      condition conformable to natural law or which will secure
      a level surface; as, moving fluids seek a level.

            When merit shall find its level.      --F. W.
                                                  Robertson.

   6. (Mech. & Surv.)
      (a) An instrument by which to find a horizontal line, or
          adjust something with reference to a horizontal line.
      (b) A measurement of the difference of altitude of two
          points, by means of a level; as, to take a level.

   7. A horizontal passage, drift, or adit, in a mine.

   {Air level}, {a spirit level}. See {Spirit level} (below).

   {Box level}, a spirit level in which a glass-covered box is
      used instead of a tube.

   {Carpenter's level}, {Mason's level}, either the plumb level
      or a straight bar of wood, in which is imbedded a small
      spirit level.

   {Level of the sea}, the imaginary level from which heights
      and depths are calculated, taken at a mean distance
      between high and low water.

   {Line of levels}, a connected series of measurements, by
      means of a level, along a given line, as of a railroad, to
      ascertain the profile of the ground.

   {Plumb level}, one in which a horizontal bar is placed in
      true position by means of a plumb line, to which it is at
      right angles.

   {Spirit level}, one in which the adjustment to the horizon is
      shown by the position of a bubble in alcohol or ether
      contained in a nearly horizontal glass tube, or a circular
      box with a glass cover.

   {Surveyor's level}, a telescope, with a spirit level
      attached, and with suitable screws, etc., for accurate
      adjustment, the whole mounted on a tripod, for use in
      leveling; -- called also {leveling instrument}.

   {Water level}, an instrument to show the level by means of
      the surface of water in a trough, or in upright tubes
      connected by a pipe.

Source : WordNet®

mason's level
     n : a level longer than a carpenter's level