Go and dance madly in a ten-sided figure (7)
I believe the answer is:
'a ten-sided figure' is the definition.
(I've seen this in another clue)
'go and dance madly' is the wordplay.
'and' means one lot of letters go next to another.
'madly' is an anagram indicator.
'go' after 'dance' is 'dancego'.
'dancego' is an anagram of 'DECAGON'.
'in' is the link.
(Other definitions for decagon that I've seen before include "Figure with 10 sides" , "Go, dance on geometric figure with ten sides" , "A polygon -- eg can-do (anag)" , "Ten-sided shape" , "10-sided figure" .)