alidade

UK: /ˈælɪˌdeɪd/, /ˈælɪˌdæd/ US: (al′i dād′)

WordReference Random House Unabridged Dictionary of American English © 2025

al•i•dade  (al′i dād′), n. [Survey.]

1. Surveying (in plane-tabling) a straightedge having a telescopic sight or other means of sighting parallel to the straightedge.
2. Surveying the entire upper part of a theodolite or transit, including the telescope, its supports, the level vials, the circle-reading device, and the spindle.

Also, al•i•dad  (al′i dad′). 

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

Collins Concise English Dictionary © HarperCollins Publishers::

alidade / ˈælɪˌdeɪd/, alidad / ˈælɪˌdæd/ 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

Etymology: 15th Century: from French, from Medieval Latin allidada, from Arabic al-'idāda the revolving radius of a circle