英语词源字典 - 在线词源网站

flash (n.1)[flash 词源字典]: 1560s, "sudden burst of flame or light," from flash (v.); originally of lightning. Figuratively (of wit, laughter, anger, etc.) from c. 1600. Meaning "period occupied by a flash, very short time" is from 1620s. Sense of "superficial brilliancy" is from 1670s. Meaning "first news report" is from 1857. The comic book character dates to 1940. Meaning "photographic lamp" is from 1913. Flash cube (remember those?) is from 1965.

Flash in the pan (1704 literal, 1705 figurative) is from old-style firearms, where the powder might ignite in the pan but fail to spark the main charge; hence figurative sense "brilliant outburst followed by failure."[flash etymology, flash origin, 英语词源]
leg-work (n.): 1891, from leg (n.) + work (n.). Originally news reporter slang for an assignment that produced more walking than text.
red (adj.2): "Bolshevik," 1917, from red (adj.1), the color they adopted for themselves. Association in Europe of red with revolutionary politics (on notion of blood and violence) is from at least 1297, but got a boost 1793 with adoption of the red Phrygian cap (French bonnet rouge) as symbol of the French Revolution. First specific political reference in English was 1848 (adj.), in news reports of the Second French Republic (a.k.a. Red Republic). Red China is from 1934. The noun meaning "radical, communist" is from 1851.