alidad

al·i·dade  (l-dd) also al·i·dad (-dd)

n.

1. An indicator or a sighting apparatus on a plane table, used in angular measurement.

2. A topographic surveying and mapping instrument used for determining directions, consisting of a telescope and attached parts.

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[French, from Medieval Latin alidada, sighting rod, from Arabic al-'ida, the revolving radius of a circle : al-, the + 'ida, revolving radius (alternate form of 'aud, humerus, from 'aada, to lop, cut (trees); see d in Semitic roots).]

Thesaurus

Noun	1.	alidad - surveying instrument consisting of the upper movable part of a theodolite including the telescope and its attachments alidade surveying instrument, surveyor's instrument - an instrument used by surveyors theodolite, transit - a surveying instrument for measuring horizontal and vertical angles, consisting of a small telescope mounted on a tripod
	2.	alidad - surveying instrument used with a plane table for drawing lines of sight on a distant object and for measuring angles alidade surveying instrument, surveyor's instrument - an instrument used by surveyors