Adamant business is steady (4)
I believe the answer is:
firm
This clue is a triple definition!
'adamant' is the first definition.
(thesaurus)
'business' is the second definition.
(firm is a kind of business)
'is steady' is the third definition.
(synonyms)
(Other definitions for firm that I've seen before include "Organization" , "Unflinching" , "corporation?" , "Steady kind of business" , "Hard" .)