To back the woman is an alternative (5)
I believe the answer is:
other
'an alternative' is the definition.
(I've seen this before)
'to back the woman' is the wordplay.
'back' shows that the letters should be reversed in order.
'the woman' becomes 'her'.
'to' back-to-front is 'ot'.
'ot'+'her'='OTHER'
'is' is the link.
(Other definitions for other that I've seen before include "Alternative - unrelated" , "Different; alternate" , "Different, disparate" , "One may be significant" , "Distinct" .)