While we could never prove it, we suspected him of duplicity, so we were never able to fully trust him despite his numerous good deeds.

what is the most likely definition of “duplicity”?

counterfeiting
cunning
determination
dishonesty

The correct answer is D. Dishonest

Explanation:

Dishonesty is defined as the opposite of honesty or disposition to deceive to someone or lie about something. This means a dishonest person might deceive or lie usually on purpose which might lead to multiple conflicts and people avoiding to trust them, thus dishonesty is considered a negative quality. In the excerpt it is mention despite there was no proof of duplicity in one specific person, they could not trust him again, this implies even if they were not sure whether he lie or deceived them, they could not trust him anymore, this can be inferred as duplicity in this context means having deceitful behavior which is behaving in a different way from what you really are and deceiving others  by doing this, which is closely connected to the definition of dishonesty as both duplicity and dishonesty aim at deceiving other people intentionally.