Unrestricted love given to writer (4)
I believe the answer is:
open
'unrestricted' is the definition.
(similar in meaning)
'love given to writer' is the wordplay.
'love' becomes 'o' (love means zero in tennis).
'given to' is a charade indicator (letters next to each other).
'writer' becomes 'pen' (something which writes).
'o'+'pen'='OPEN'
(Other definitions for open that I've seen before include "Not yet decided - to start" , "Frank; unfold" , "Not enclosed" , "ready to entertain new ideas" , "Frank - unsettled" .)