Firm stayed in chaos (6)
I believe the answer is:
steady
'firm' is the definition.
(I know that firm can be written as steady)
'stayed in chaos' is the wordplay.
'in chaos' is an anagram indicator.
'stayed' with letters rearranged gives 'STEADY'.
(Other definitions for steady that I've seen before include "Not liable to fluctuation" , "Firmly supported, stable" , "Motionless" , "not easily shaken" , "Hey" .)