Etymology
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black market (n.)
"unauthorized dealing in restricted or rationed commodities," 1931, from black (adj.), probably suggesting "dark, invisible" or "shady, improper" + market (n.). As an adjective by 1935. It exploded in popularity with the coming of World War II rationing.
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stock market (n.)
"place where securities are bought and sold," 1809, from stock (n.2) + market. The original Stock Market (mid-14c.) was a fish and meat market in the City of London on or near the later site of Mansion House, so called perhaps because it occupied the site of a former stocks. Stock exchange is attested from 1773.
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flea market (n.)
1910, especially in reference to the marché aux puces in Paris, so-called "because there are so many second-hand articles sold of all kinds that they are believed to gather fleas." [E.S. Dougherty, "In Europe," 1922].
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hoi polloi (n.)
1837, from Greek hoi polloi (plural) "the people," literally "the many" (plural of polys, from PIE root *pele- (1) "to fill"). Used in Greek by Dryden (1668) and Byron (1822), in both cases preceded by the, even though Greek hoi means "the," a mistake repeated often by subsequent writers who at least have the excuse of ignorance of Greek. Ho "the" is from PIE *so- "this, that" (nominative), cognate with English the and Latin sic. From the adjective agoraios "pertaining to the agora; frequenting the market" Greek had hoi agoraioi "loungers in the market, loafers, common, low men."
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ad valorem 
type of customs duties based on the market value of goods at the original place of shipment, 1711, Modern Latin, "(in proportion) to the value," from ad "to" (see ad-) + Late Latin valorem, accusative of valor "value" (see value (n.)). Sometimes abbreviated ad val.
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Jazz Age 

1921; see jazz (n.); popularized 1922 in writings of F. Scott Fitzgerald; usually regarded as the years between the end of World War I (1918) and the Stock Market crash of 1929.

We are living in a jazz age of super-accentuated rhythm in all things; in a rhythm that (to "jazz" a word) is super-normal, a rhythm which is the back-flare from the rhythm of a super war. ["Jacobs' Band Monthly," Jan. 1921]
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