It stops the flow of dry hair (7)
I believe the answer is:
airlock
'it stops the flow' is the definition.
The definition suggests a singular noun which matches the answer.
'dry hair' is the wordplay.
'dry' becomes 'air' (airing is a kind of drying).
'hair' becomes 'lock' (a lock of hair).
'air'+'lock'='AIRLOCK'
'of' acts as a link.
Can you help me to learn more?
(Other definitions for airlock that I've seen before include "Bubble obstructing flow" , "plumbing problem" , "chamber?" , "obstruction" .)