Rush with a stem concealed (5)
I believe the answer is:
haste
'rush' is the definition.
('haste' can be a synonym of 'rush')
'with a stem concealed' is the wordplay.
'concealed' indicates the answer is hidden within the clue.
'HASTE' can be found hidden inside 'with a stem'.
(Other definitions for haste that I've seen before include "furious activity" , "Rash speed" , "Expeditiousness" , "Possible cause of careless mistakes?" , "Urgency of action" .)