Lake or pond (4)
I believe the answer is:
mere
I believe this clue is a double definition.
'lake' is the first definition.
(I know that mere is a type of lake)
'pond' is the second definition.
(I know that mere is a type of pond)
(Other definitions for mere that I've seen before include "DDwater" , "Nothing more than a small pool" , "Lake in Cumbria" , "Pond, only what is said" , "Just an English lake" .)