Something that’s conspiratorial involves a secret plan with other people. A conspiratorial glance between siblings is bound to make their babysitter nervous.
Things done in a conspiratorial way are secretive and sneaky: a meet up between spies is conspiratorial, and several coworkers planning a surprise party for their boss might spend the day communicating in various conspiratorial ways. The adjective comes from its related verb, conspire, “plot,” or “make secret plans,” from the Latin root conspirare, “to agree, unite, or plot,” or literally, “to breathe together.”
relating to or characteristic of conspiracy or conspirators“a