Tube stop (4)
I believe the answer is:
stem
I believe this is a double definition.
'tube' is the first definition.
(stem is a kind of tube)
'stop' is the second definition.
(stemming is a kind of stopping)
(Other definitions for stem that I've seen before include "Halt flow" , "Slender upright part, of flower or glass" , "part of vegetable?" , "Slender upright part, of flower or wineglass" , "something growing?" .)