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' (abbreviation for id est, 'that is' in Latin).
'covered by' is an insertion indicator.
'garfunkel' becomes 'art' (Art Garfunkel of Simon and Garfunkel).
'cheers' becomes 'ta' (both can informally mean thank you).
'ie' placed within '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" .)