Ăl'i-dāde, n.

n. [Ar. al-hudāt, a sort of rule, from hudaj, to guide on the right way; L. Lat. alidada, alhidada.] The index of a graduated instrument, as a quadrant or astrolabe, carrying the sights or telescope, and showing the degrees cut off on the arc of the instrument. Whewell.

. Alidade level, the spirit level attached to the alidade of an astronomical instrument (as a meridian circle) for adjusting its zero with reference to the horizon.