Favour Romeo over compiler mostly (7)
I believe the answer is:
rosette
'favour' is the definition.
('favour' historically meant a token of affection)
'romeo over compiler mostly' is the wordplay.
'romeo' becomes 'r' (phonetic alphabet: alpha, bravo, charlie etc.).
'over' becomes 'o' (cricket abbreviation**).
'compiler' becomes 'setter' (both can mean a writer of crosswords).
'mostly' means to remove the last letter.
'setter' with its last letter taken away is 'sette'.
'r'+'o'+'sette'='ROSETTE'
(Other definitions for rosette that I've seen before include "Type of award" , "Ribbon badge for prize-winner" , "Equestrian prize" , "Prize adornment" , "Horse show award" .)