alidade

American  

[al-i-deyd] / ˈæl ɪˌdeɪd /

Also alidad

noun

Surveying.

1. (in plane-tabling) a straightedge having a telescopic sight or other means of sighting parallel to the straightedge.

2. the entire upper part of a theodolite or transit, including the telescope, its supports, the level vials, the circle-reading device, and the spindle.

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alidade British  

/ ˈælɪˌdæd, ˈælɪˌdeɪd /

noun

1. a surveying instrument used in plane-tabling for drawing lines of sight on a distant object and taking angular measurements

2. the upper rotatable part of a theodolite, including the telescope and its attachments

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Etymology

Origin of alidade

1400–50; variant of alhidade < Medieval Latin alhidada < Arabic al-ʿiḍādah the turning radius (like a clock hand) of a circle; replacing late Middle English allydatha (< Old Spanish alhidada )

Example Sentences

Escutia crouched down in front of his alidade - an age-old, compass-based device - and sighted the fire: 152 degrees, southwest.

From BBC • Aug. 15, 2022

The complete instrument would also have had a rotating pointer, called an alidade, mounted on a pin running through the central hole.

From Economist • Oct. 26, 2017

This axle is provided with an endless screw that gears with a toothed sector, and the latter controls the rotatory axis of the alidade.

From Scientific American Supplement, No. 363, December 16, 1882 by Various

One of the telescopes is then placed over its alidade and moves with it; and the apparatus thus comprehends only a system of synchronous movements.

From Scientific American Supplement, No. 363, December 16, 1882 by Various

An additional article of the sketcher's equipment is a holder for his pencils, alidade, eraser, knife, pins, etc.

From Manual of Military Training Second, Revised Edition by Moss, James A. (James Alfred)