Scope, some would say, for discharge (5)

I believe the answer is:

rheum

I'm a little stuck... Click here to teach me more about this clue!

'for discharge' is the definition.
(I've seen this before)

I cannot understand how the remainder of the clue works.

(Other definitions for rheum that I've seen before include "Rhubarb genus; a head cold" , "Watery stuff" , "Watery mucous discharge" , "runny nose" , "Catarrh" .)

I've seen this clue in The Times.

Want a hint initially instead of a full solution? Install my app