Some gunpowder, say, for crook (3,4)
I believe the answer is:
tea leaf
I believe this is a double definition.
'some gunpowder say' is the first definition.
(gunpowder is a type of tea)
'crook' is the second definition.
(tea leaf is Cockney rhyming slang for a thief)
'for' acts as a link.
(Other definitions for tea leaf that I've seen before include "one exhibiting a fortune?" , "One from Assam perhaps" , "Couple" , "ending up in hot water" , "Cockney crook" .)