- a line serving as a base
- any starting or reference point, figure, amount, level, etc. with which others can be measured or compared
- Surveying a horizontal line measured with special accuracy to provide a base for survey by triangulation
- ☆ Baseball the unmarked lane, six feet (1.8 m) wide, between any two consecutive bases: a base runner must normally stay within this lane
- Basketball end line; esp., an area of the court just inside this line
- Tennis the line at the back at either end of the court
See base line in American Heritage Dictionary 4
or base·line noun
a. A line serving as a basis, as for measurement, calculation, or location.
b. A measurement, calculation, or location used as a basis for comparison.
- Baseball The base path.
a. The boundary line at either end of a court, as in basketball or tennis.
b. The area near this boundary line: made a basket from the base line.
c. A style of play in tennis in which the player remains near the base line and rarely approaches the net.
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