Mermaid's habitat (3)
I believe the answer is:
sea
'mermaid's habitat' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for sea that I've seen before include "E.g. Yellow, Red area" , "Large expanse of water" , "Ocean area" , "Adriatic, for example" , "& 14 Ozone" .)