Constant way to stop flow (7)
I believe the answer is:
staunch
'constant' is the definition.
(similar in meaning)
'way to stop flow' is the wordplay.
I cannot quite see how this works, but
'way' could be 'st' (abbreviation for street) and 'st' is found in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for staunch that I've seen before include "Arrest" , "Hearty" , "Reliable" , "Loyal and dependable - stem the flow" , "Loyal; restrict (a flow of blood)" .)