Plant stalk (4)
I believe the answer is:
stem
'plant stalk' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for stem that I've seen before include "Stalk; restrict (a flow)" , "Stalk; stop (flow)" , "Staunch - support" , "Staunch (flow)" , "Ski turn and plant stalk" .)