Pool contributing to summer entertainment (4)
I believe the answer is:
mere
'pool' is the definition.
(mere is a kind of pool)
'contributing to summer entertainment' is the wordplay.
'contributing to' says the answer is hidden in the clue.
'MERE' is hidden within 'summer entertainment'.
(Other definitions for mere that I've seen before include "bathing may be permitted in this?" , "Nothing more than a small pool" , "Pond, only what is said" , "Without additions or modifications" , "Lake; simple" .)