Stream from the said opening (4)
I believe the answer is:
pour
'stream' is the definition.
('pour' can be a synonym of 'stream')
'the said opening' is the wordplay.
'the said' indicates a 'sounds like' (homophone) clue.
'opening' becomes 'pore' (pore is a kind of opening).
'pore' sounds like 'POUR'.
'from' is the link.
(Other definitions for pour that I've seen before include "(Of rain) fall heavily" , "Cause to flow or rain heavily" , "Dispense tea - rain hard" , "Cause to flow in a stream" , "Teem" .)