Webster's Revised Unabridged Dictionary (1913)
An instrument for taking altitudes, as a quadrant, sextant, etc.
Webster's Revised Unabridged Dictionary (1913), edited by Noah Porter. About
hEnglish - advanced version
\al*tim"e*ter\ (&?;), n. [ll. altimeter; altus high + metrum, gr. &?;, measure: cf. f. altimètre.] an instrument for taking altitudes, as a quadrant, sextant, etc.
VFA-13 Aviation Glossary
An onboard instrument which senses air pressure in order to gauge altitude.
Aviation - English - Spintra.com
A device to measure altitude, either barometric altitude or radar altitude
Abbreviation Airbus A340
Altimeter: This instrument measures the aircraft altitude by using the static pressure.