Pool nothing more (4)
I believe the answer is:
mere
I believe this clue is a double definition.
'pool' is the first definition.
(mere can mean a lake)
'nothing more' is the second definition.
(I've seen this before)
(Other definitions for mere that I've seen before include "Simply, nothing more than" , "Insignificant" , "Pierre's mother identified" , "of no significance" , "Just an English lake" .)