Merman in some secret hell-hole (5)
I believe the answer is:
ethel
'merman' is the definition.
(I've seen this in another clue)
'some secret hell-hole' is the wordplay.
'some' indicates the answer is hidden within the clue (some of the parts of the word are used).
'ETHEL' is hidden within 'secret hell hole'.
'in' acts as a link.
(Other definitions for ethel that I've seen before include "Trying not to be seen" , "Lady" , "girl" , "Dame --- Smyth; William Brown's sister" , "woman" .)