Search for a very long time (6)
I believe the answer is:
forage
'search' is the definition.
(I know that forage is a type of search)
'for a very long time' is the wordplay.
'a very long time' becomes 'age' (I've seen this before).
'for'+'age'='FORAGE'
(Other definitions for forage that I've seen before include "Hunt for food or provisions" , "Search widely for food" , "Wander and feed" , "Go searching, perhaps for food" , "sort of cap" .)