Online Etymology Dictionary

Philadelphia: city in Pennsylvania, U.S., from Gk., taken by William Penn to mean lit. "brotherly love," from philos "loving" + adelphos "brother" (see Adelphi). Also the name recalls that of the ancient city in Lydia, mentioned in the N.T., which was so called in honor of Attalos II Philadelphos, 2c B.C.E. king of Pergamon, who founded it. His title is said to have meant "loving the brethren." Slang shortening Philly first attested 1891; Philadelphia lawyer "clever, shrewd attorney" attested from 1788 in London, said originally to have been applied to Andrew Hamilton, who obtained the famous acquittal of J.P. Zenger on libel charges in 1735.
"[C]ricket and coaching were after all popular in their day in places besides Philadelphia. It was merely that Philadelphia kept on with them longer than most places. This is a perennial Philadelphia trick, and gives to Philadelphia a sort of perpetual feeling of loss. Philadelphians are always just now getting rid of things that are picturesque, like those gas lamps on the streets, only because everybody else got rid of them long ago." [Nathaniel Burt, "The Perennial Philadelphians," 1963]
allergic: 1911, from allergy (q.v.); fig. use, "antipathetic, repulsed" is from 1937; first ref. is to Philadelphia scrapple.
yo: as a greeting, 1859, but the word is attested as a sailor's or huntsman's utterance since c.1420. Modern popularity dates from World War II (when, it is said, it was a common response at roll calls) and seems to have been most intense in Philadelphia.
Stetson: 1902, trademark name, from John B. Stetson (1830-1906), U.S. hat manufacturer, who started his company in Philadelphia in 1865.
Federalist: "member or supporter of the Federal party in U.S. politics," originally of supporters of the Philadelphia constitution, 1787, from federal.
congressman: 1780, in ref. to U.S. Congress, and it first appears in a piece of abuse (written by a Loyalist):
"Ye coxcomb Congressmen, declaimers keen, Brisk puppets of the Philadelphia scene ..."
autoharp: 1882, name on a patent taken out by Charles F. Zimmermann of Philadelphia, U.S.A., for an improved type of harp, an instrument considerably different from the modern autoharp, actually a chord zither, which was invented about the same time by K.A. Gütter of Markneukirchen, Germany, who called it a Volkszither.
wisteria: 1819, formed by botanist Thomas Nuttall, Eng. botanist, in allusion to Amer. anatomist Caspar Wistar (1761-1818) of Philadelphia. The -e- apparently is a misprint.
Main Line: "principal line of a railway," 1841; meaning "affluent area of residence" is 1930s, originally that of Philadelphia, from the "main line" of the Pennsylvania Railroad which added local stops to a string of backwater towns west of the city late 19c. that helped turn them into fashionable suburbs. Meaning "principal vein into which drugs can be injected" is 1933, Amer.Eng. slang; the verb in this sense is from 1934.
hoagie: Amer.Eng. (originally Philadelphia) "hero, large sandwich made from a long, split roll," originally hoggie (c.1936), traditionally said to be named for Big Band songwriter Hoagland Howard "Hoagy" Carmichael (1899-1981), but the use of the word pre-dates his celebrity and the original spelling seems to suggest another source. Modern spelling is c.1945, and may have been altered by influence of Carmichael's nickname.
Conestoga: 1699, name of an Indian tribe in southcentral Pennsylvania, probably from some Iroquoian language and sometimes said to mean "people of the cabin pole;" later a place in Lancaster County, Pennsylvania, where a characteristic type of covered wagon was built. Conestoga wagon is from 1750 (about three years before the last of the Conestoga Indians were massacred), but it was already an established term as the first reference is to the name of a Philadelphia tavern. Also a breed of horses (1824) and a type of boot and cigar (see stogie).
mummer: c.1405, probably a fusion of M.Fr. momeur "mummer" (from momer "mask oneself," from momon "mask") and M.E. mommen "to mutter, be silent," related to mum (interj.). OED marks it as "obsolete," but the word, and the custom, are alive and thriving in Philadelphia, U.S.A.
ginkgo: 1773, from Japanese ginkyo, from Chinese yin-hing, from yin "silver" + hing "apricot" (Sino-Japanese kyo). Introduced to New World 1784 by William Hamilton in his garden near Philadelphia. One was planted 1789 at Pierce Arboretum (now part of Longwood Gardens) in Kennett Square, Pa., and by 1968 it was 105 ft. tall.
slink: O.E. slincan "to creep, crawl" (of reptiles), from P.Gmc. *slenkanan (cf. Swed. slinka "to glide," Du. slinken "to shrink, shrivel;" related to sling (v.)). Of persons, attested from late 14c. Slinky (adj.) "sinuous and slender," of women or clothes, first attested 1921. As a proprietary name for a spring marketed as a toy, 1948, by James Industries Inc., Philadelphia, U.S.A.
booze: 1768 "drink a lot" (v.), from M.E. bouse (c.1300), from M.Du. busen "to drink heavily," related to M.H.G. bus (intrans.) "to swell, inflate," of unknown origin. The noun is first recorded 1859, reinforced by name of Philadelphia distiller E.G. Booze. Boozy was one of Benjamin Franklin's 225 synonyms for "drunk," published in 1722. In New Zealand from c.WWII, a drinking binge was a boozeroo.
scrod: 1841, "young cod, split and fried or boiled," possibly from Du. schrood "piece cut off," from M.Du. scrode "shred" (cf. O.E. screade, see shred). If this is the origin, the notion is probably of fish cut into pieces for drying or cooking.
A Boston brahmin is on a business trip to Philadelphia. In search of dinner, and hungry for that Boston favorite, broiled scrod, he hops into a cab and asks the driver, "My good man, take me someplace where I can get scrod." The cabbie replies, "Pal, that's the first time I've ever been asked that in the passive pluperfect subjunctive."
liberty: late 14c., from O.Fr. liberté "freedom," from L. libertatem (nom. libertas) "freedom, condition of a freeman," from liber "free" (see liberal)
"The spirit of liberty is the spirit which is not too sure it is right." [Learned Hand, 1944]
Nautical sense of "leave of absence" is from 1758. To take liberties "go beyond the bounds of propriety" is from 1625. Sense of "privileges" led to sense of "a person's private land" (mid-15c.), which yielded sense in 18c. England and America of "a district within a county but having its own justice of the peace," and also "a district adjacent to a city and in some degree under its municipal jurisdiction" (e.g. Northern Liberties of Philadelphia).
hero: 1387, "man of superhuman strength or courage," from L. heros "hero," from Gk. heros "demi-god" (a variant singular of which was heroe), originally "defender, protector," from PIE base *ser- "to watch over, protect" (cf. L. servare "to save, deliver, preserve, protect"). Sense of "chief male character in a play, story, etc." first recorded 1697. Fem. form heroine first attested 1659, from L. heroina, from Gk. heroine. First record of hero-worship is from 1774. Heroic verse (1617), decasyllabic iambic, is from It. Hero, the New York term for a sandwich elsewhere called submarine, grinder, poor boy (New Orleans), or hoagie (Philadelphia), is 1955, origin unknown, perhaps folk etymology of Gk. gyro, a type of sandwich.
thou: 2nd nominative singular personal pronoun, O.E. þu, from P.Gmc. *thu (cf. O.Fris. thu, M.Du., M.L.G. du, O.H.G., Ger. du, O.N. þu, Goth. þu), from PIE *tu-, second person singular pronoun (cf. L. tu, Ir. tu, Welsh ti, Gk. su, Lith. tu, O.C.S. ty, Skt. twa-m). Superseded in M.E. by plural form you (from a different root), but retained in certain dialects (e.g. Philadelphia Quakers). The plural at first was used in addressing superior individuals, later also (to err on the side of propriety) strangers, and ultimately all equals. By c.1450 the use of thou to address inferiors gave it a tinge of insult unless addressed by parents to children, or intimates to one another. Hence the verb meaning "to use 'thou' to a person" (c.1440).
"Avaunt, caitiff, dost thou thou me! I am come of good kin, I tell thee!" ["Hickscorner," c.1530]
A brief history of the second person pronoun in Eng. can be found here.
knight: O.E. cniht "boy, youth, servant," common W.Gmc. (cf. O.Fris. kniucht, Du. knecht, M.H.G. kneht "boy, youth, lad," Ger. Knecht "servant, bondman, vassal"), of unknown origin. Meaning "military follower of a king or other superior" is from c.1100. Began to be used in a specific military sense in Hundred Years War, and gradually rose in importance through M.E. period until it became a rank in the nobility 16c. The verb meaning "to make a knight of (someone)" is from c.1300. Knighthood is O.E. cnihthad "the period between childhood and manhood;" sense of "rank or dignity of a knight" is from c.1300. The chess piece so called from c.1440. Knight in shining armor is from 1965. Knights of Columbus, society of Catholic men, founded 1882 in New Haven; Knights of Labor, trade union association, founded in Philadelphia, 1869; Knights of Pythias, secret order, founded in Washington, 1864.