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' says the answer is hidden in the clue.
'RIVER' is hidden in the letters of '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" .)