Duplicity
Etymology
From Latin duplicitas, "doubleness," from duplex, "twofold," combining duo, "two," and plicare, "to fold." The literal sense is being folded in two — one surface visible, another hidden beneath. Duplicity keeps that geometry exactly: a person doubled, showing one face and concealing its opposite.
noun · /doo-PLIS-ih-tee/
Deceitfulness in which a person says or shows one thing while secretly intending or doing another.
What it names
The two-faced vice of maintaining a false front — presenting one self to the world while another operates behind it.
Example
Her duplicity became clear when the same memo she praised in the meeting turned up, savaged, in her notes to the board.
Related idea
Hypocrisy is professing virtues or beliefs you do not hold; duplicity is the more active double-dealing of pursuing hidden aims behind a false face.