Source : Webster's Revised Unabridged Dictionary (1913)

Altimeter \Al*tim"e*ter\, n. [LL. altimeter; altus high +
   metrum, Gr. ?, measure: cf. F. altim[`e]tre.]
   An instrument for taking altitudes, as a quadrant, sextant,
   etc. --Knight.

Source : WordNet®

altimeter
     n : an instrument that measures the height above ground; used in
         navigation