Plural of mobster; criminals who are members of organized crime syndicates or gangs.
From 'mob' (crowd/organized group of people) plus '-ster' (person, often derogatory). The 'mob' term became synonymous with organized crime.
The word 'mobster' is 20th-century American slang that became standard through Hollywood movies. It's interesting that we use the word 'mob' from Latin 'mobile vulgus' (fickle crowd) to mean organized crime.
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