seditious adj.

mid-14c., sedicioun, "rebellion, uprising, revolt, factitious commotion in the state; concerted attempt to overthrow civil authority; violent strife between factions, civil or religious disorder, riot; rebelliousness against authority," from Old French sedicion (14c., Modern French sédition) and directly from Latin seditionem (nominative seditio) "civil disorder, dissension, strife; rebellion, mutiny," literally "a going apart, separation." This is from sed- "without, apart, aside" (see se-) + itio "a going," from ire "to go" (from PIE root *ei- "to go").

In early use, 'factious with tumult, turbulent' (J.); now chiefly, engaged in promoting disaffection or inciting to revolt against constituted authority [OED]

The meaning "conduct or language inciting to rebellion against a lawful government" is attested by 1838. Less serious than treason, as wanting an overt act.

But it is not essential to the offense of sedition that it threaten the very existence of the state or its authority in its entire extent. Thus, there are seditious assemblies, seditious libels, etc., as well as direct and indirect threats and acts amounting to sedition — all of which are punishable as misdemeanors by fine and imprisonment. [Century Dictionary]

Latin seditio was glossed in Old English by unsib, folcslite.