Attractive boyfriend returned suitable uniform to league (9)
I believe the answer is:
beautiful
'attractive' is the definition.
(similar in meaning)
'boyfriend returned suitable uniform to league' is the wordplay.
'boyfriend' becomes 'beau' (synonyms).
'returned' shows that the letters should be reversed in order.
'suitable' becomes 'fit' (similar in meaning).
'uniform' becomes 'U' (phonetic alphabet: alpha, bravo, charlie etc.).
'to league' becomes 'l' (abbreviation).
'fit' reversed gives 'tif'.
'beau'+'tif'+'u'+'l'='BEAUTIFUL'
(Other definitions for beautiful that I've seen before include "Comely" , "Pleasing to the eye" , "Visually pleasing" , "Nice to see" , "Very pleasant to behold" .)