Tolerate a stream (5)
I believe the answer is:
Here is my best explanation:
This clue is a double definition.
'tolerate' is the first definition.
('brook' can be a synonym of 'tolerate')
'a stream' is the second definition.
(brook is a kind of stream)
(Other definitions for brook that I've seen before include "Stand for", "Stream; put up with", "running water", "stomach", "Small fresh-water stream", "Allow" and "Bear - small stream".)