A hole-in-corner sort of entertainer (7)
I believe the answer is:
crooner
'entertainer' is the definition.
(crooner is a kind of entertainer)
'a hole-in-corner sort' is the wordplay.
'a hole' becomes 'o'.
'in' means one lot of letters goes inside another.
'sort' indicates an anagram.
'corner' is an anagram of 'croner'.
'o' inserted into 'croner' is 'CROONER'.
'of' is the link.
(Other definitions for crooner that I've seen before include "Crosby-type singer" , "Profession of Bing, Frank or Perry" , "Singer of sentimental songs" , "Sentimental balladeer" , "Singer like Bing and Frank" .)