Etymology
Advertisement
flapper (n.)

1560s, "one who or that which flaps," agent noun from flap (v.). Sense of "forward young woman" is 1921 slang, but the exact connection is disputed. Perhaps from flapper "young wild-duck or partridge" (1747), with reference to flapping wings while learning to fly, many late 19c. examples of which are listed in Wright's "English Dialect Dictionary" (1900), including one that defines it as "A young partridge unable to fly. Applied in joke to a girl of the bread-and-butter age."

Other suggested sources include a late 19c. northern English dialectal use of the word for "teen-age girl" (on notion of one with the hair not yet put up), or an earlier meaning "prostitute" (1889), which is perhaps from dialectal flap "young woman of loose character" (1610s). Any or all of these might have converged in the 1920s sense. Wright also has flappy, of persons, "wild, unsteady, flighty," with the note that it also was "Applied to a person's character, as 'a flappy lass,'" and further on he lists flappy sket (n.) "an immoral woman." In Britain the word took on political tones in reference to the debate over voting rights.

"Flapper" is the popular press catch-word for an adult woman worker, aged twenty-one to thirty, when it is a question of giving her the vote under the same conditions as men of the same age. [Punch, Nov. 30, 1927]
Related entries & more 
Advertisement
flabbergast (v.)
1772, flabbergasted, mentioned (with bored) in a magazine article that year as a new vogue word, of uncertain origin. Perhaps from some dialect (in 1823 flabbergast was noted as a Sussex word), perhaps ultimately an arbitrary formation alluding to flabby or flapper and aghast. "Like many other popular words expressing intensity of action, ... not separable into definite elements or traceable to a definite origin" [Century Dictionary]. Related: Flabbergasted; flabbergasting; flabbergastation.
Related entries & more 
bat (n.2)
flying mouse-like mammal (order Chiroptera), 1570s, a dialectal alteration of Middle English bakke (early 14c.), which is probably related to Old Swedish natbakka, Old Danish nathbakkæ "night bat," and Old Norse leðrblaka "bat," literally "leather flapper," from Proto-Germanic *blak-, from PIE root *bhlag- "to strike" (see flagellum). If so, the original sense of the animal name likely was "flapper." The shift from -k- to -t- may have come through confusion of bakke with Latin blatta "moth, nocturnal insect."

Old English word for the animal was hreremus, from hreran "to shake" (see rare (adj.2)), and rattle-mouse, an old dialectal word for "bat," is attested from late 16c. Flitter-mouse (1540s) is occasionally used in English (variants flinder-mouse, flicker-mouse) in imitation of German fledermaus "bat," from Old High German fledaron "to flutter."

As a contemptuous term for an old woman, it is perhaps a suggestion of witchcraft (compare fly-by-night), or from bat as "prostitute who plies her trade by night" [Farmer, who calls it "old slang" and finds French equivalent "night swallow" (hirondelle de nuit) "more poetic"].
Related entries & more 
shimmy (v.)

"do a suggestive dance," 1918, perhaps via phrase shake the shimmy, which is possibly from shimmy (n.), a U.S. dialectal form of chemise (mistaken as a plural; compare shammy) which is attested by 1837. Or perhaps the verb is related to shimmer (v.) via a notion of glistening light. The transferred sense of "vibration of a motor vehicle" is by 1925. Related: Shimmied; shimmying. As a noun, the name of a popular, fast, suggestive pre-flapper dance, by 1919.

The first "shimmy" dance to appear, almost simultaneously with the signing of the armistice, was greeted with a howl of derision. "Vulgar"! cried the sensitive; "Absurd"! was the verdict of the scornful; "Difficult, but darned attractive!" modern art expressed it. Then, the "shimmy" in its rightful form was presented by Gilda Grey in the Shubert extravaganza "The Gaieties of 1919". Result: a lawsuit with a rival theatrical producer, and the awakened interest of everybody in the much-discussed and condemned dance. ["Good Morning Judge! 'Shake Your Shimmy,'" in The Greenville (S.C.) News, Aug. 27, 1919]
Related entries & more