Arrive, running in stream (5)
I believe the answer is:
river
'stream' is the definition.
(river is a kind of stream)
'arrive running in' is the wordplay.
'in' indicates a hidden word.
'RIVER' is hidden within 'arrive running'.
(Other definitions for river that I've seen before include "Slow-cooked meat dish" , "x or y, so to speak" , "Flowing water" , "Such as the Nile or Amazon" , "Waterway" .)