Perfidious (9)
I believe the answer is:
dishonest
'perfidious' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for dishonest that I've seen before include "Untrustworthy" , "Deceitful - hedonists (anag)" , "Insincere" , "shady" , "shifty" .)