Saint in love with wealthy bird (7)
I believe the answer is:
ostrich
'bird' is the definition.
(I know that ostrich is a type of flightless bird)
'saint in love with wealthy' is the wordplay.
'saint' becomes 'st' (abbreviation).
'in' indicates putting letters inside.
'love' becomes 'o' (love means zero in tennis).
'with' means one lot of letters go next to another.
'wealthy' becomes 'rich' (similar in meaning).
'o'+'rich'='orich'
'st' put inside 'orich' is 'OSTRICH'.
(Other definitions for ostrich that I've seen before include "Torch is held over large bird" , "The head-in-the-sand bird" , "Emu-like bird" , "Largest extant bird" , "with a big nest egg" .)