Fabulous quartet not entirely without rhythm (7)
I believe the answer is:
beatles
'fabulous quartet not entirely without rhythm' is the definition.
I can't tell whether this definition defines the answer.
'fabulous quartet not entirely without' is the wordplay.
'fabulous quartet' becomes 'beat' (I can't explain this - if you can you should give a lot more credence to this answer).
'not entirely' means to remove the last letter.
'without' becomes 'less' (I've seen this in another clue).
'less' with its last letter taken away is 'les'.
'beat'+'les'='BEATLES'
Can you help me to learn more?
(Other definitions for beatles that I've seen before include "The Fab Four composer-singers" , "John, Paul, Ringo and George - collectively" , "Best ale for the Liverpudlian group" , "British pop band of the 60s" , "Lee bats for the band, oddly" .)