Source : Webster's Revised Unabridged Dictionary (1913)

Theodolite \The*od"o*lite\, n. [Probably a corruption of the
   alidade. See {Alidade}.]
   An instrument used, especially in trigonometrical surveying,
   for the accurate measurement of horizontal angles, and also
   usually of vertical angles. It is variously constructed.

   Note: The theodolite consists principally of a telescope,
         with cross wires in the focus of its object glass,
         clamped in Y's attached to a frame that is mounted so
         as to turn both on vertical and horizontal axes, the
         former carrying a vernier plate on a horizontal
         graduated plate or circle for azimuthal angles, and the
         latter a vertical graduated arc or semicircle for
         altitudes. The whole is furnished with levels and
         adjusting screws and mounted on a tripod.

Source : WordNet®

theodolite
     n : a surveying instrument for measuring horizontal and vertical
         angles, consisting of a small telescope mounted on a
         tripod [syn: {transit}]