almucantar (?ælm??kænt?) or almacantarn1. (Astronomy) a circle on the celestial sphere parallel to the horizontal plane2. an instrument for measuring altitudes[C14: from French, from Arabic almukantar?t sundial]Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014almucantarA circle on the celestial sphere that is parallel to the horizontal plane.Dictionary of Unfamiliar Words by Diagram Group Copyright © 2008 by Diagram Visual Information Limited