Underhand, untrustworthy (9)
I believe the answer is:
deceitful
I believe this is a double definition.
'underhand' is the first definition.
(thesaurus)
'untrustworthy' is the second definition.
(thesaurus)
(Other definitions for deceitful that I've seen before include "Duplicitous" , "Dishonest" , "unreliable" , "cheating" , "Untruthful" .)