Old song: "Crazy About a Girl" (8)
I believe the answer is:
madrigal
'old song' is the definition.
(I've seen this before)
'crazy about a girl' is the wordplay.
'crazy' becomes 'mad' (synonyms).
'about' is an anagram indicator.
'a'+'girl'='agirl'
'agirl' anagrammed gives 'rigal'.
'mad'+'rigal'='MADRIGAL'
(Other definitions for madrigal that I've seen before include "air" , "glee" , "Part-song" , "Elaborate part song" , "Without exaggeration" .)