Strengthen, with "up" (4)
I believe the answer is:
beef
'strengthen with up' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for beef that I've seen before include "Bovine flesh" , "Brawn; grumble" , "Type of meat" , "Complain; meat" , "Strength - grievance" .)