Not confident in a truce, wavering after intervention by knight (9)
I believe the answer is:
uncertain
'not confident' is the definition.
(I've seen this before)
'in a truce wavering after intervention by knight' is the wordplay.
'wavering' is an anagram indicator.
'after intervention by' means one lot of letters goes inside another (to intervene can mean to become involved in).
'knight' becomes 'n' (chess).
'in'+'a'+'truce'='inatruce'
'inatruce' with letters rearranged gives 'ucertain'.
'ucertain' enclosing 'n' is 'UNCERTAIN'.
(Other definitions for uncertain that I've seen before include "dubious" , "Not completely confident or sure of" , "Doubtful, indecisive" , "up in the air" , "Not at all sure or decided" .)