Definition of alidade in US English:



  • A sighting device or pointer for determining directions or measuring angles, used in surveying and (formerly) astronomy.

    • ‘In the circle an index on the alidades gives the angle that they form with the vertical diameter.’
    • ‘A wide variety of alidades and plane tables are available, both in manual and electronic versions.’
    • ‘Both the alidades and the straight edges of the quadrant are fitted with viewers.’
    • ‘A pointer, called an alidade, was pivoted at the centre of the disk.’
    • ‘Telescopic alidades came into use in Europe in the early 1800s, and were soon introduced to American practice.’


Late Middle English: directly or (in modern use) via French and Spanish from Arabic al-‘iḍāda ‘the revolving radius’, probably based on aḍud ‘upper arm’.