Seditious is the adjective that goes with sedition. It describes speech, writing, or actions meant to push people to disobey or fight a government: a seditious speech, a seditious pamphlet, seditious talk. A person can be called seditious too, though that sounds even more like a courtroom or a history book. Same serious, legal flavour as sedition. Younger everyday English more often says rebellious or anti-government unless the legal meaning is the point. Though actually, like sedition, people argue over the word: one side hears a real call to break the state; the other hears a government trying to make protest sound like a crime.