al·i·dade 
(ălĭ-dād′) also al·i·dad (-dăd′)
(ălĭ-dād′) also al·i·dad (-dăd′)n.
1. An indicator or a sighting apparatus on a plane table, used in angular measurement.
2. A topographic surveying and mapping instrument used for determining directions, consisting of a telescope and attached parts.
[French, from Medieval Latin alidada, sighting rod, from Arabic al-'iḍāda, the revolving radius of a circle : al-, the + 'iḍāda, revolving radius (alternate form of 'aḍud, humerus, from 'aḍada, to lop, cut (trees); see ʿd in the Appendix of Semitic roots).]