Stable; poised (8)
I believe the answer is:
balanced
This clue is a double definition.
'stable' is the first definition.
(similar in meaning)
'poised' is the second definition.
('balance' can be a synonym of 'poise')
(Other definitions for balanced that I've seen before include "Equipoised" , "With weight evenly distributed, or equalised" , "Having weight equally distributed" , "Steady - objective" , "Having different elements in the correct proportions, in a diet say" .)