seditious (adj.)

mid-14c., "rebellion, uprising, revolt, 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," from se- "apart" (see secret (n.)) + itio "a going," from ire "to go" (from PIE root *ei- "to go").

Meaning "conduct or language inciting to rebellion against a lawful government" is from 1838. An Old English word for it was folcslite. 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" [Century Dictionary].