Consistent stable (6)
I believe the answer is:
steady
I believe this clue is a double definition.
'consistent' is the first definition.
(thesaurus)
'stable' is the second definition.
(similar in meaning)
(Other definitions for steady that I've seen before include "Not shaking or moving" , "Changeless, constant" , "Reliable, unvarying" , "Not wavering" , "Get a grip!" .)