'rabble-rouser' is a compound formed in English from the noun 'rabble' (meaning 'a noisy or disorderly crowd') plus the verb 'rouse' (meaning 'to stir up, awaken') with the agentive suffix '-er'.

'rabble' entered Middle English (as 'rable' or similar forms) from Old French influences meaning 'crowd' (exact ultimate origin uncertain), and 'rouse' comes from Middle English verbs meaning 'to awaken or stir up'; combining these elements produced the compound 'rabble-rouser' in modern English usage (recorded from the 19th century onward).

Initially it referred specifically to someone who stirred up a disorderly crowd; over time it has retained that sense and is now commonly used more broadly for anyone who incites public feeling or unrest, often in a political context.