Counter for pressure unit (3)
I believe the answer is:
bar
I believe this is a double definition.
'counter' is the first definition.
(bar is a kind of counter)
'pressure unit' is the second definition.
(bar is a kind of pressure unit)
'for' acts as a link.
(Other definitions for bar that I've seen before include "Stop" , "Public house" , "Bank, shoal" , "Lawyers may be called to it" , "A pub counter or iron rod" .)