Anne is unstable, mad (6)
I believe the answer is:
insane
'mad' is the definition.
(similar in meaning)
'anne is unstable' is the wordplay.
'unstable' is an anagram indicator.
'anne'+'is'='anneis'
'anneis' with letters rearranged gives 'INSANE'.
(Other definitions for insane that I've seen before include "Mentally unhinged" , "Quite mad" , "Wild < cuckoo < cracked" , "Mental" , "out to lunch" .)