noun
Etymology: base (I)
: a main line taken as or representing a base: as
a. : base 6b ; specifically : a line extending east and west from a chosen reference point on a principal meridian and forming with the meridian a pair of coordinate axes for locating township and section corners — used in United States public-land surveying
b. : the line joining the base piece and the base point in artillery fire
c. : the lowest horizontal line in a profile drawing of a ship used as a base for vertical measurements
d. of a perspective drawing : the line formed by the intersection of the ground plane and the picture plane
e. : the area within which a baseball player must keep when running between bases
f. : the back line at each end of a tennis court — see tennis illustration
g. : the lower horizontal guideline for aligning capitals in freehand lettering
h. : a known quantity used as a control for further experimentation