late 15c. (Caxton), "capable of movement, capable of being moved, not fixed or stationary," from Old French mobile (14c.), from Latin mobilis "movable, easy to move; loose, not firm," figuratively, "pliable, flexible, susceptible, nimble, quick; changeable, inconstant, fickle," contraction of *movibilis, from movere "to move" (from PIE root *meue- "to push away"). Sociology sense of "able to move into different social levels" is by 1927. Mobile home "large trailer permanently parked and used as a residence" is recorded by 1936. Mobile phone is by 1983.

A long-distance number tapped into an Illinois Bell car telephone glowed red on a display. Satisfied that the digits were correct, I pushed the SEND button on the phone. Familiar beeps and boops emerged from the handset. Then, before a half block of this Chicago suburb had slipped by, I was in contact with my New York office. ["Take-along Telephones," Popular Science, October 1983]

early 15c. in astronomy, "outer sphere of the universe" (the primum mobile), from mobile (adj.); the artistic sense "abstract sculpture consisting of parts suspended so as to move," associated with Alexander Calder, is by 1939, perhaps a shortening of mobile sculpture (1936). Now-obsolete sense of "the common people, the rabble" (1670s, short for Latin mobile vulgus) led to mob (n.). Middle English had moble, moeble (mid-14c.) "movable goods, personal property," from Old French moble, meuble, from the Latin adjective, but in 16c. this was replaced by furniture.

"the first source of motion," mid-15c., from Medieval Latin (11c.), literally "the first movable thing;" see prime (adj.) + mobile.

In the Ptolemaic system of astronomy, the tenth or outermost of the revolving spheres of the universe, which was supposed to revolve from east to west in twenty-four hours, and to carry the others along with it in its motion; hence, any great or first source of motion. [Century Dictionary]

A translation of Arabic al-muharrik al-awwal "the first moving" (Avicenna). Englished by Chaucer as the firste Moeuyng (c. 1400). Old science also had primum frigidum "pure cold: an elementary substance, according to the doctrine of Parmenides."

1833 in the military sense of "prepare for active operation or taking the field;" 1838 as "render capable of movement;" 1846 as "bring into readiness or circulation," from French mobiliser, from mobile "movable" (see mobile (adj.)). Related: Mobilized; mobilizing.

early 15c., "capacity for motion, ability to move or be moved, property of being easily movable," from Old French mobilité "changeableness, inconsistency, fickleness" and directly from Latin mobilitatem (nominative mobilitas) "activity, speed," figuratively "changeableness, fickleness, inconstancy," from mobilis "movable, easy to move" (see mobile (adj.)). Socio-economics sense of "possibility of movement between different social levels" is from 1900 in sociology writing.

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.