Group's joke entertaining any number (4)
I believe the answer is:
gang
'group's' is the definition.
(gang is a kind of group)
'joke entertaining any number' is the wordplay.
'joke' becomes 'gag' ('gag' can be a synonym of 'joke'**).
'entertaining' is an insertion indicator.
'any number' becomes 'n' (I've seen this in other clues).
'gag' placed around 'n' is 'GANG'.
(Other definitions for gang that I've seen before include "Work, criminal, group" , "set of tools" , "Maybe criminal group" , "A lot of labourers" , "Go (Scot)" .)