"Waterloo” group (4)
I believe the answer is:
abba
'waterloo group' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for abba that I've seen before include "Palindromic Swedish pop group who sang ` `Waterloo' '" , "Eurovision prizewinning Swedish pop group" , "Pater's" , "Biblical pop" , "Swedish pop music group" .)