Challenge — stand up to (4)
I believe the answer is:
defy
I believe this is a double definition.
'challenge' is the first definition.
(I know that defy is a more specific form of the action challenge)
'stand up to' is the second definition.
(I've seen this before)
(Other definitions for defy that I've seen before include "Refuse to obey (person)" , "Brave" , "Flout" , "Stand against" , "Challenge or resist" .)