On fire, love bird (8)
I believe the answer is:
flamingo
'bird' is the definition.
(flamingo is a kind of bird)
'on fire love' is the wordplay.
'on fire' becomes 'flaming' (synonyms).
'love' becomes 'o' (love means zero in tennis).
'flaming'+'o'='FLAMINGO'
(Other definitions for flamingo that I've seen before include "colourful bird" , "Tall wading bird" , "Pink flier" , "Large pink bird" , "Wading bird with pink and red plumage" .)