Antonym of “ingenuous” is:

The antonym of "ingenuous" is "Disingenuous." The word "ingenuous" describes someone who is innocent, unsuspecting, and candid, often implying a lack of sophistication or worldliness. It suggests sincerity and straightforwardness. Therefore, its opposite would describe someone who is not sincere or candid.

• "Disingenuous" is the direct antonym, meaning not candid or sincere, typically by pretending that one knows less about something than one really does. It implies a subtle form of dishonesty or craftiness, directly opposing the open and honest nature of ingenuousness.
• "Naive" is a synonym for "ingenuous," meaning lacking experience, wisdom, or judgment, and often implies innocence.
• "Honest" and "Sincere" are also synonyms or closely related positive traits associated with "ingenuous," describing someone truthful and genuine. They do not represent the opposite meaning.