A street or area in London historically famous for merchants selling cheap goods; now used generally to refer to a place associated with low-quality merchandise.
Cheap plus side (as in the side of a city/street). Cheapside was an actual medieval and early modern London street specializing in cheap goods. The name became generic for discount shopping areas.
Cheapside actually exists in London's financial district today, but it's now surrounded by expensive banks—it's a perfect example of how place names preserve the economic history of cities, even after the landscape completely changes.
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