A person, especially a street vendor or peddler, who sells cheap or worthless goods, or something of poor quality; also an adjective meaning shoddy or dishonest.
Cheap plus jack (a common name used derisively for ordinary people). Historically, many common names became labels for types (like 'tom' in tomcat)—'jack' was used similarly to suggest a common rogue or trickster.
Before the internet, 'cheapjack' referred to traveling peddlers who'd follow fairs and markets—today it's a perfectly preserved word for a social role that barely exists anymore, like how 'tinker' and 'ragman' are now museum pieces of occupation history.
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