#straight_angle  an angle of 180 degrees
  supertype:  angular_unit__angularunit  a unit of measurement for angles
  part of:  circumference
  part:  quadrant.angular_unit__right_angle__rightangle  a quarter of the circumference of a circle
     part:  grad__grade  one-hundredth of a right angle
     part:  oxtant  a unit of angular distance equal to half a quadrant
        part:  arcdegree__degree  a measure for arcs and angles; "there are 360 degrees in a circle"
           part:  minute_of_arc__minute__arcminute  a unit of angular distance equal to a 60th of a degree
              part:  arcsecond__second  a 60th part of a minute of arc; "the treasure is 2 minutes and 45 seconds south of here"

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