Song that is covered by Garfunkel cheers (7)
I believe the answer is:
arietta
'song' is the definition.
(arietta is a kind of song)
'that is covered by garfunkel cheers' is the wordplay.
'that is' becomes 'ie' (short for Latin 'id est', 'that is').
'covered by' means one lot of letters goes inside another.
'garfunkel' becomes 'art' (Art Garfunkel of Simon and Garfunkel).
'cheers' becomes 'ta' (both can informally mean thank you).
'ie' put inside 'art' is 'ariet'.
'ariet'+'ta'='ARIETTA'
(Other definitions for arietta that I've seen before include "Little aria" , "number from opera" , "Little song" , "Item by 6 [VERDI]" , "Short operatic song" .)