The Collaborative International Dictionary of English v.0.48:
Leveling \Lev"el*ing\, n. [Written also levelling.]
1. The act or operation of making level.
2. (Surveying) The art or operation of using a leveling
instrument for finding a horizontal line, for ascertaining
the differences of level between different points of the
earth's surface included in a survey, for establishing
grades, etc., as in finding the descent of a river, or
locating a line of railroad.
Leveling instrument. See Surveyor's level, under Level,
Leveling staff, a graduated rod or staff used in connection
with a leveling instrument for measuring differences of
level between points.