Stop, obstruct (7)
I believe the answer is:
occlude
This clue is a double definition.
'stop' is the first definition.
(thesaurus)
'obstruct' is the second definition.
(I know that obstruct can be written as occlude)
(Other definitions for occlude that I've seen before include "Close up (an orifice or passage)" , "Shut out, obscure" , "Block, obstruct" , "Cut or shut off" , "Stop up, obstruct" .)