Insufficient silver in pool (6)
I believe the answer is:
meagre
'insufficient' is the definition.
(associated in meaning)
'silver in pool' is the wordplay.
'silver' becomes 'Ag' (Ag is the chemical symbol for silver).
'in' indicates putting letters inside.
'pool' becomes 'mere' (mere can mean a lake).
'ag' placed within 'mere' is 'MEAGRE'.
(Other definitions for meagre that I've seen before include "Lean; lacking in quality" , "Poor in quality" , "Lean, thin" , "Insufficient; scanty" , "Thin -- inadequate" .)