A hole-in-the corner sort of singer (7)
I believe the answer is:
crooner
'singer' is the definition.
(I've seen this before)
'a hole-in-the corner sort' is the wordplay.
'a hole' becomes 'o'.
'in the' means one lot of letters goes inside another.
'sort' indicates anagramming the letters.
'corner' anagrammed gives 'croner'.
'o' placed within 'croner' is 'CROONER'.
'of' acts as a link.
(Other definitions for crooner that I've seen before include "Singer of sentimental songs" , "Crosby-type singer" , "Singer of quiet songs" , "Crosby or Sinatra?" , "Sentimental balladeer" .)