Solitary type must entertain fellow Cockney? (8)
I believe the answer is:
londoner
'cockney?' is the definition.
(cockney is a kind of Londoner)
'solitary type must entertain fellow' is the wordplay.
'solitary type' becomes 'loner' (I've seen this before).
'must entertain' indicates putting letters inside.
'fellow' becomes 'don' (I've seen this before).
'loner' placed around 'don' is 'LONDONER'.
(Other definitions for londoner that I've seen before include "Native of the great wen" , "Native of Camberwell, perhaps" , "Resident of the UK capital" , "Native of Notting Hill or Camden, say" , "who uses capital for home?" .)