Impressive characters in winkle-pickers (4)
I believe the answer is:
epic
'impressive' is the definition.
(I've seen this before)
'characters in winkle-pickers' is the wordplay.
'characters in' indicates the answer is hidden within the clue.
'EPIC' can be found hidden inside 'winkle pickers'.
(Other definitions for epic that I've seen before include "Long account" , "Long poem, book, film" , "blockbuster" , "Colossal" , "long poem telling of heroic deeds" .)