(n.) 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.
Meaning of LEVEL in English
Webster's English dictionary. Английский словарь Webster. 2012