(æb) 

    An altazimuth instrument, specially designed by M. Antoine d'Abbadie [from whom it is said to be named] for determining the latitude without the use of the artificial horizon required by the sextant on land, and also for determining small angular heights and true bearings of terrestrial objects, without the trouble occasioned by the sextant.
 
  1876 S. Kens. Loan Coll. Catal. (ed. 3) 747 A person familiar with the use of the sextant only, on observing circum~meridian altitudes for his first attempt with the aba, obtained his latitude to within 4´´. 1879 Daily News 23 Aug. 4/4 The chief instrument he [an African explorer] used was the sextant, but he also used the aba.