Fab Four (7)
I believe the answer is:
beatles
'fab four' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for beatles that I've seen before include "Famous pop group" , "John, Paul, Ringo and George - collectively" , "1960s' Liverpool rock group" , "Able set? (anag)" , "Be least among fabulous four" .)