Love enormous Greek character (5)
I believe the answer is:
omega
'greek character' is the definition.
(letter from the Greek alphabet)
'love enormous' is the wordplay.
'love' becomes 'o' (love means zero in tennis).
'enormous' becomes 'mega ' (I've seen this before).
'o'+'mega'='OMEGA'
(Other definitions for omega that I've seen before include ""The Alpha and the ___"" , "long letter" , "Last (Gk. letter)" , "Greek character symbolizing resistance" , "24th Greek letter" .)