Insincere (3-5)
I believe the answer is:
two-faced
'insincere' is the definition.
(similar in meaning)
This is all the clue.
(Other definitions for two-faced that I've seen before include "Double-dealing, like Janus?" , "Deceitful, with double visage" , "Duplicitous" , "Treacherous" , "Hypocritical (like clock in tower?)" .)