Check support for such technical subjects (4)
I believe the answer is:
stem
'check' is the definition.
(both can mean to control or stop)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for stem that I've seen before include "Staunch (flow)" , "feature of wine glass" , "Restrain the flow of" , "Check - part of a plant" , "Stop or slow the flow of" .)