'alidade' originates from Arabic, specifically the word 'al-ʿiḍāda,' where 'al-' meant 'the' and 'ʿiḍāda' meant 'the arm of a balance.'

'al-ʿiḍāda' transformed into the Medieval Latin word 'alhidada,' and eventually became the modern English word 'alidade.'

Initially, it meant 'the arm of a balance,' but over time it evolved into its current meaning of 'a sighting device on surveying instruments.'