Famous boxer with boy or girl (6)
I believe the answer is:
alison
'girl' is the definition.
'famous boxer with boy' is the wordplay.
'famous boxer' becomes 'ali' (I've seen this in another clue).
'with' is a charade indicator (letters next to each other).
'boy' becomes 'son' (synonyms).
'ali'+'son'='ALISON'
'or' acts as a link.
(Other definitions for alison that I've seen before include "Girl's name" , "woman" , "female" , "lady" , "Girl" .)