The noun duplicity means to say different things to two people.
Synonyms are artifice, dishonesty, deceit, or hypocrisy.
The word origins from Old French (early 15th century) duplicite meaning “deceptiveness, character or practice of speaking differently of the same thing or acting differently at different times or to different persons”. It also comes from Late Latin duplicitatem (13th century) meaning “doubleness”.
She’d seen his duplicity on many occasions.
They were blamed for duplicity in their dealings with both sides.
His profession was marked by obvious duplicity.