'rumor-monger' originates from English, specifically from combining 'rumor' and 'monger', where 'rumor' comes from Latin 'rumor' meaning 'noise, gossip' and 'monger' is from Old English/Middle English words meaning 'seller' or 'dealer'.

'rumor' comes from Latin 'rumor' (meaning 'noise, gossip'), entered English via Old French/Latin use; 'monger' comes from Old English/Middle English 'mangere'/'mongere' meaning 'seller'. The compound pattern (noun + -monger) became productive in Middle and Modern English (e.g., 'scandalmonger', 'warmonger'), producing 'rumor-monger' in modern usage.

Initially 'monger' implied a literal seller or dealer; over time the compound came to mean not a seller but a person who 'deals in' or spreads something (here, rumors). 'Rumor-monger' therefore evolved from the image of a 'seller of rumors' to the current meaning 'one who spreads rumors or gossip'.