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

The alidade is a triangular ruler with one or more working scales on it beside other measurements.

From Military Instructors Manual by Schoonmaker, Oliver

It consists of a frame in the form of an octant having a graduated scale upon its arc, and an index arm, or alidade pivoted at its apex.

From The Gutenberg Webster's Unabridged Dictionary Section P and Q by Project Gutenberg

Always carry several large-headed pins using one at your present station and resting the side of the alidade against it, swinging the other end for sighting.

From Military Instructors Manual by Schoonmaker, Oliver