IPA: /ˈɡæŋstər/
KK: /ˈɡæŋstɚ/
A person who is part of a group involved in illegal activities, often associated with organized crime.
The police arrested several gangsters during the raid.
Gangster → The word originates from the American English term 'gang' (meaning a group of people) combined with the suffix '-ster' (meaning a person associated with). A gangster is thus a person who is part of a group, often involved in criminal activities.
Think of a 'group' ('gang') of people and remember that a 'gangster' is someone who is part of that group, often involved in illicit activities.