Clue: Hooker, one sounding rough? (4)
Answer: BURR
Explanation: Definition: Hooker
Double definition: a hooked seed-case of a plant such as cleavers or burdock, and a rough throaty r sound (I think that the question mark might cover the doubtful 'one', referring to the sound, or to the word 'hooker', which could be pronounced with a burr if you are so inclined).