Etymology
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mob-cap (n.)

a type of woman's indoor cap with a bag-shaped crown and a broad band and frills, 1795 (as simply mob, 1748), from cap (n.) + obsolete mob (n.) "negligent attire" (1660s), earlier "a strumpet" (earlier form mab, 1550s), which is related to the obsolete verb mob "to tousle the hair, to dress untidily" (1660s), and perhaps is ultimately from mop (n.), but has been influenced by Mab as a female name. Dutch has a similar compound, mopmuts, but the relationship between it and the English word is uncertain.

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mob (v.)

"to attack in a mob, crowd round and annoy or beset," transitive, 1709, from mob (n.). Meaning "to form into a mob" is from 1711. Related: Mobbed; mobbing.

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mob (n.)

1680s, "disorderly part of the population, rabble, common mass, the multitude, especially when rude or disorderly; a riotous assemblage," slang shortening of mobile, mobility "common people, populace, rabble" (1670s, probably with a conscious play on nobility), from Latin mobile vulgus "fickle common people" (the Latin phrase is attested c. 1600 in English), from mobile, neuter of mobilis "fickle, movable, mobile" (see mobile (adj.)).

Mob is a very strong word for a tumultuous or even riotous assembly, moved to or toward lawlessness by discontent or some similar exciting cause. Rabble is a contemptuous word for the very lowest classes, considered as confused or without sufficient strength or unity of feeling to make them especially dangerous. [Century Dictionary, 1897]

Also used of a promiscuous aggregation of people in any rank of life (1680s), and in Australia and New Zealand used without disparagement for "a crowd." Meaning "gang of criminals working together" is from 1839, originally of thieves or pick-pockets; the American English sense of "organized crime in general" is from 1927.

The Mob was not a synonym for the Mafia. It was an alliance of Jews, Italians, and a few Irishmen, some of them brilliant, who organized the supply, and often the production, of liquor during the thirteen years, ten months, and nineteen days of Prohibition. ... Their alliance — sometimes called the Combination but never the Mafia — was part of the urgent process of Americanizing crime. [Pete Hamill, "Why Sinatra Matters," 1998]

Mob scene "crowded place" is by 1922, from earlier use in reference to movies and theatrical productions; mob-rule "ochlocracy" is by 1806.

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cap (v.)

c. 1400, "to put a cap on," from cap (n.); meaning "cover as with a cap" is from c. 1600. Figurative sense of "complete, consummate, bring to a climax" is from 1580s; that of "go one better, outdo, excel" is by 1821. Related: Capped; capping. To cap verses (1610s) was "to quote alternately verses each beginning with the same letter with which the last ended."

The capping of Latin verses is a common game in classical schools. No verse may be used twice, and no hesitation or delay is permitted; so that a moderate proficiency in the game supposes several thousand verses arranged in the memory alphabetically. [Century Dictionary, 1895]
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cap (n.)

late Old English cæppe "hood, head-covering, cape," a general Germanic borrowing (compare Old Frisian and Middle Dutch kappe, Old High German chappa) from Late Latin cappa "a cape, hooded cloak" (source of Spanish capa, Old North French cape, French chape), a word of uncertain origin. Possibly a shortened from capitulare "headdress," from Latin caput "head" (from PIE root *kaput- "head").

The Late Latin word apparently originally meant "a woman's head-covering," but the sense was transferred to "hood of a cloak," then to "cloak" itself, though the various senses co-existed. Old English took in two forms of the Late Latin word, one meaning "head-covering," the other "ecclesiastical dress" (see cape (n.1)). In most Romance languages, a diminutive of Late Latin cappa has become the usual word for "head-covering" (such as French chapeau).

Meaning "soft, small, close-fitted head covering" in English is from early 13c., originally for women; extended to men late 14c. Extended to cap-like coverings on the ends of anything (such as hubcap) from mid-15c. Meaning "contraceptive device" is first recorded 1916.

Meaning "cap-shaped piece of copper lined with gunpowder and used to ignite a firearm" is by 1825, hence cap-gun (1855); extended to paper version used in toy pistols, 1872 (cap-pistol is from 1879).

Figurative thinking cap is from 1839 (considering cap is 1650s). Cap and bells (1781) was the insignia of a fool; cap and gown (1732) of a scholar. To set one's cap at or for (1773) means "use measures to gain the regard or affection of," usually in reference to a woman seeking a man's courtship.

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ice-cap (n.)

"a general or continuous permanent covering of a certain area of land, whether large or small, with snow or ice, especially in the arctic regions," 1859 in geology, from ice (n.) + an extended sense of cap (n.).

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cap-a-pie (adj.)

"all over" (in reference to dress or armor), 1520s, from French cap-à-pie, literally "head to foot." The more usual French form is de pied en cap. The French words are from Latin caput "head" (from PIE root *kaput- "head") + pedem "foot" (from PIE root *ped- "foot").

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mobocracy (n.)

"mob rule, government by the disorderly classes," 1754, a hybrid from mob (n.) + -cracy "rule or government by." Related: Mobocrat "leader of a mob, a demagogue" (1798); mobocratic.

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kepi (n.)
soldier's peaked cap, 1861, from French képi (19c.), from German Swiss käppi, diminutive of German Kappe "a cap," from Late Latin cappa "hood, cap" (see cap (n.)). The usual style of uniform cap in the American Civil War.
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