In Valparaiso I left some stain (4)
I believe the answer is:
soil
'some stain' is the definition.
(synonyms)
'in valparaiso i left' is the wordplay.
'in' indicates a hidden word.
'SOIL' is hidden in the letters of 'valparaiso i left'.
(Other definitions for soil that I've seen before include "Dirty - dirt" , "refuse" , "Loose upper layer of earth" , "Earth; make dirty" , "Earth for growing" .)