ˈaləˌdād noun
also al·i·dad -ˌdad
( -s )
Etymology: alteration (influenced by French alidade ) of Middle English allidatha, from Medieval Latin alhidada, from Arabic al-'iḍādah the revolving radius of a circle
: a rule equipped with simple or telescopic sights and used for determination of direction: as
a. : a part of an astrolabe
b. : the ruler of a plane table
c. : a part of a surveying instrument (as a transit) consisting of the telescope, the telescope standards, the plate levels, the vernier and associated magnifiers, and the spindle
d. : a telescope mounted on a compass repeater and used as part of a ship's navigational equipment for taking bearings