altimeter

n. instrument for measuring altitude

An altimeter is an active instrument used to measure the altitude of an object above a fixed level. The measurement of altitude is called altimetry, which is related to the term bathymetry, the measurement of depth underwater.
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Noun
1. an instrument that measures the height above ground; used in navigation
(hypernym) measuring instrument, measuring system, measuring device
(hyponym) hypsometer
(part-meronym) aneroid barometer, aneroid

n. altimeter, instrument for measuring altitude

(n.)
An instrument for taking altitudes, as a quadrant, sextant, etc.