Al"i*dade (&?;), n. [LL. alidada, alhidada, fr. Ar. al-'idāda a sort of rule: cf. F. alidade.] The portion 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.

• a sighting device used for measuring angles