The altitude of the base of a mass of cloud; measured by a ceilometer.

(sports) An extreme sport consisting of jumping from a fixed structure on land, using a parachute.

present participle of BASE jump

plural of base unit

A unit of measurement which is not itself defined in terms of other units, and from which other units may be derived. / The main unit of a computer or hi-fi system.

plural of base case

The part of a recursive definition or algorithm that is not defined in terms of itself.

plural of base year

plural of base runner

(baseball, softball) A play where a runner on any base runs to the next base, usually while the pitcher pitches to a batter. Such a runner is liable to be put out if tagged with the ball while not in contact with any base.