Dictionary.net

• 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

2010 - New Age Dictionary Database
By Oddity Software

• 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

1913 - Webster's Revised Unabridged Dictionary
By Noah Webster.