Regular shape of old cape with label on (7)
I believe the answer is:
octagon
'regular shape' is the definition.
(as in a regular octagon)
'old cape with label on' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'cape' becomes 'c' (abbreviation used on maps).
'with' is a charade indicator (letters next to each other).
'label' becomes 'tag' (synonyms).
'o'+'c'+'tag'+'on'='OCTAGON'
'of' is the link.
(Other definitions for octagon that I've seen before include "Eight-sided object" , "Eight-sided figure" , "Figure of many sides" , "Figure with 8 sides" , "Eight-sided room" .)