Boy takes midnight air (4)
I believe the answer is:
song
'air' is the definition.
(thesaurus)
'boy takes midnight' is the wordplay.
'boy' becomes 'son' ('son' can be a synonym of 'boy'**).
'takes' is a charade indicator (letters next to each other).
'midnight' becomes 'g'.
'son'+'g'='SONG'
(Other definitions for song that I've seen before include "Musical composition; air" , "Musical rendition" , "Melody (which is cheap to go for)" , "Musical number" , "Piece of music, usually with words" .)