Merman or Waters (5)
I believe the answer is:
ethel
I believe this clue is a double definition.
'merman' is the first definition.
(I've seen this before)
'waters' is the second definition.
(I've seen this in another clue)
(Other definitions for ethel that I've seen before include "- Barrymore, actress" , "girl" , "Perhaps a Barrymore" , "Dame - Smyth, Eng. composer, suffragette" , "- Merman, US musical comedy star" .)