Merriam-Webster's Word of the Day for August 23, 2023 is:

duplicity • \doo-PLISS-uh-tee\  • noun

Duplicity is a formal word that refers to dishonest behavior meant to trick or deceive someone.

// The extent of his duplicity wasn't clear until a century after his death, when documents revealing more of his many deceptions were discovered.

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Examples:

“Series three ended with a bang—patriarch Logan Roy (Brian Cox, in one of TV's most memorable performances) doing the dirty on his children and rewriting his divorce settlement to rob them of boardroom power at the family firm, just as they were about to wrest control from him. And, the kicker, he was able to do it thanks to the duplicity of son-in-law Tom (Matthew Macfadyen).” — Chris Bennion, The Daily Telegraph (London), 25 May 2023

Did you know?

We’ve all probably dealt with someone who acted a little two-faced—they said one thing and did another, for example, or they talked “from both sides of their mouth.” If such behavior has made you do a double take or left you feeling double-crossed, you may be single-minded in your quest to learn more about duplicity. Duplicity comes from a long line of “double” talk, starting with its Latin ancestor duplex, which means “double” or “twofold.” Duplex is also the source of the English word duplex (which can be a noun meaning “a two-family house” or an adjective meaning “double”), and it is the root of another term for doubling it up, duplicate.