bobby soxyoudaoicibaDictYouDict[bobby sox 词源字典]
1943, from diminutive of bob (n.2) + sox. So called because they are "shortened" compared to knee-socks. Derivative bobby-soxer first attested 1944.
Months ago colored bobby sox folded at the top were decreed, not by anyone or any group but, as usual, by a sudden mysterious and universal acceptance of the new idea. Now no teen-ager dares wear anything but pure white socks without a fold. ["Life" magazine, Dec. 11, 1944]
[bobby sox etymology, bobby sox origin, 英语词源]
flapper (n.)youdaoicibaDictYouDict
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]
poser (n.)youdaoicibaDictYouDict
"one who practices an affected attitude," 1881, agent noun from pose (v.1); revived in teen-ager slang by 1983. Meaning "question that puzzles" is from 1793 from pose (v.2); earlier it meant "one who asks testing questions" (1580s).
teen (n.)youdaoicibaDictYouDict
"teen-aged person," 1818 (but rare before 20c.), from -teen. As an adjective meaning "of or for teen-agers," from 1947.
teenage (adj.)youdaoicibaDictYouDict
also teen age, teen-age; 1911, from teen + age (n.). Originally in reference to Sunday School classes. Teen-aged (adj.) is from 1922.
teenager (n.)youdaoicibaDictYouDict
also teen ager, teen-ager; 1922, derived noun from teenage (q.v.). The earlier word for this was teener, attested in American English from 1894, and teen had been used as a noun to mean "teen-aged person" in 1818, though this was not common before 20c.
teens (n.)youdaoicibaDictYouDict
1670s (plural), "teen-age years of a person," formed from -teen taken as a separate word. As "decade of years comprising numbers ending in -teen," from 1889.