Settled partnership? (4)
I believe the answer is:
firm
I believe this is a double definition.
'settled' is the first definition.
(similar in meaning)
'partnership?' is the second definition.
(I've seen this before)
(Other definitions for firm that I've seen before include "commercial partnership" , "Resolute kind of business" , "A steady business enterprise? (4)" , "Hard" , "Resistant to pressure" .)