Stream or boring river (7)
I believe the answer is:
torrent
'stream' is the definition.
(I know that torrent is a type of stream)
'or boring river' is the wordplay.
'boring' is an insertion indicator (some letters must 'bore' a hole into other letters).
'river' becomes 'trent' (River Trent).
'or' placed inside 'trent' is 'TORRENT'.
(Other definitions for torrent that I've seen before include "Outburst" , "Violently fast stream of water" , "Turbulent stream of water" , "Heavy flow of water" , "Heavy stream" .)