Plug firm (7)
I believe the answer is:
staunch
This clue is a double definition.
'plug' is the first definition.
(I've seen this before)
'firm' is the second definition.
(I've seen this before)
(Other definitions for staunch that I've seen before include "solid" , "Stop bleeding; trusty" , "Firm; stem" , "act to stop bleeding" , "Firm in loyalty" .)