Green’s Dictionary of Slang

mob n.2

also mobb, mobocracy
[abbr. mobile vulgus, the fickle crowd, mob was a term cited by Swift in 1712 as one of those that should be purged from the language. Surprisingly Johnson, whose Dict. (1755) eschewed (inter alia) dumfound, ignoramus and touchy allowed it]

1. [late 17C+] the rabble, the city proletariat [SE f. 1800].

2. [early 19C+] a company or group of associates; occas. of non-human groups.

3. [mid-19C+] a criminal gang.

4. [mid-19C+] a gang of ruffians or thugs.

5. [1920s+] (US) constr. with the, the US Mafia.

6. [1990s+] by ext., e.g. in UK, any form of organized crime.

7. see mobster n.

In derivatives

mobism (n.)

[mid-19C] the phenomenon of the mob.

mob-handed (adv.) [-handed adj.]

[1930s+] accompanied by a large gang.

In compounds

mobman (n.)

[1930s] (Aus. Und.) a member of a criminal gang.