alidade

Where does the word "alidade" come from? It comes from Arabic al-'idada, passing through Medieval Latin before entering English (1400s).

Alidade’s story begins in Arabic: al-'idada meant “the pointer, rule.” Literally "the revolving radius" or pointer of a measuring circle. By 1400s, the word had taken hold in Medieval Latin as alhidada. The sighting rule of the astrolabe, known to Europe through Arabic treatises translated in Spain. It reached English by 1400s as alidade. Entered English as the name for the sighting arm of a surveying instrument. Today, alidade means the sighting device on a surveying or astronomical instrument used to measure angles and directions.

1. Stage 1 · Arabic · medieval al-'idada "the pointer, rule", literally "the revolving radius" or pointer of a measuring circle.
2. Stage 2 · Medieval Latin · 1400s alhidada "sighting rule", the sighting rule of the astrolabe, known to Europe through Arabic treatises translated in Spain.
3. Stage 3 · English · 1400s alidade "sighting device for angle measurement", entered English as the name for the sighting arm of a surveying instrument.