Moose Oil: that's rocking song (1,4,3)
'song' is the definition.
(I've seen this before)
'moose oil that's rocking' is the wordplay.
'that's rocking' indicates an anagram.
'moose'+'oil'='mooseoil'
'mooseoil' is an anagram of 'O SOLE MIO'.
(Other definitions for o sole mio that I've seen before include "Neapolitan song" , "Italian original of Presley's It's Now or Never" , "It's Now or Never used this Italian song" , "Italian song anglicised as It's Now or Never" , "Air" .)
'song' is the definition.
(I've seen this before)
'moose oil that's rocking' is the wordplay.
'that's rocking' indicates anagramming the letters.
'moose'+'oil'='mooseoil'
'mooseoil' with letters rearranged gives 'O SOLE MIO'.