No ex-hag could possibly have such a figure! (7)
I believe the answer is:
hexagon
'such a figure' is the definition.
(hexagon is a kind of figure)
'no ex-hag could possibly' is the wordplay.
'could possibly' indicates an anagram.
'no'+'ex'+'hag'='noexhag'
'noexhag' anagrammed gives 'HEXAGON'.
'have' acts as a link.
(Other definitions for hexagon that I've seen before include "Six-sided polygon" , "A six-sided geometric figure" , "there are several sides to it" , "Shape of a honeycomb cell" , "Six-sided shape" .)