Possible Clues:

• Half a cross a round
• Straight line from circle's centre to circumference
• Figure that's squared in a common formula
• Line from centre of circle to circumference
• Line from centre of circle
• Raid botched over American range of operation
• Distance from centre to circumference of circle
• The 'r' of 'pi r squared'
• Bone; half diameter
• Bone connecting the elbow to the wrist