Deceitful, disloyal (11)
I believe the answer is:
treacherous
I believe this is a double definition.
'deceitful' is the first definition.
(thesaurus)
'disloyal' is the second definition.
(similar in meaning)
(Other definitions for treacherous that I've seen before include "Not to be trusted" , "Disloyal; dangerous" , "Unreliable" , "Perfidious" , "Not true" .)