Crossword Genius

Stop - this is a hold-up (4)

Ross

I believe the answer is:

stem

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'stop' is the definition.
(I know that stem is a more specific form of the action check)

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for stem that I've seen before include "Shoot; arrest" , "Main central part as of plant or glass" , "'Stalk, shank (4)'" , "Dam" , "Restrain - staunch - supporter" .)

I've seen this clue in The Globe and Mail.
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