Girl without love shows ambition (4)
I believe the answer is:
goal
'ambition' is the definition.
(I've seen this in another clue)
'girl without love' is the wordplay.
'girl' becomes 'gal' (synonyms).
'without' means one lot of letters goes inside another ('without' can be similar in meaning to 'outside').
'love' becomes 'o' (love means zero in tennis).
'gal' enclosing 'o' is 'GOAL'.
'shows' is the link.
(Other definitions for goal that I've seen before include "End" , "... destination (at football?)" , "Objective or score" , "Something to be achieved" , "Target or ambition" .)