Ring about tie-on label on figure (7)
I believe the answer is:
octagon
'figure' is the definition.
(octagon is a kind of figure)
'ring about tie-on label on' is the wordplay.
'ring' becomes 'o'.
'about' becomes 'c' (abbreviation for 'circa'**).
'tie-on label' becomes 'tag' (I've seen this before).
'o'+'c'+'tag'+'on'='OCTAGON'
(Other definitions for octagon that I've seen before include "Eight-sided room" , "Geometric figure with eight sides" , "Eight-sided shape" , "plane figure" , "Eight sided figure" .)