The Collaborative International Dictionary of English v.0.48:
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.
Somebody there of his own level. --Swift.
Be the fair level of thy actions laid
As temperance wills and prudence may persuade.
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.
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
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
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.