Old saint entertained by instrument for Elvis (8)
I believe the answer is:
costello
'elvis' is the definition.
Both the answer and definition are singular nouns.
Perhaps there's an association between them I don't understand?
'old saint entertained by instrument' is the wordplay.
'old' becomes 'o' (abbreviation).
'saint' becomes 'st' (abbreviation).
'entertained by' is an insertion indicator (inserted letters are hosted or entertained).
'instrument' becomes 'cello' (cello is a kind of instrument).
'o'+'st'='ost'
'ost' going into 'cello' is 'COSTELLO'.
'for' acts as a link.
Can you help me to learn more?
(Other definitions for costello that I've seen before include "Elvis -, British singer, songwriter" , "Rock singer" .)