Duplicitous (3-5)
I believe the answer is:
two-faced
'duplicitous' is the definition.
(I know that duplicitous can be written as two-faced)
This is all the clue.
(Other definitions for two-faced that I've seen before include "Deceitful, with double visage" , "Showing a double-sided visage to deceive" , "Deceitful or insincere - on the double?" , "Treacherous" , "Hypocritical, like Janus" .)