Mafia vs gangdom

Mafia and gangdom both are nouns.

Word	Noun	Adjective	Verb	Adverb
Mafia	Yes	No	No	No
gangdom	Yes	No	No	No

As nouns, gangdom is a hypernym of Mafia; that is, gangdom is a word with a broader meaning than Mafia:

Mafia: a secret terrorist group in Sicily; originally opposed tyranny but evolved into a criminal organization in the middle of the 19th century
gangdom: underworld organizations

Other hypernyms of Mafia include gangland, organized crime.

Mafia (noun)	gangdom (noun)
a crime syndicate in the United States; organized in families; believed to have important relations to the Sicilian Mafia	underworld organizations
a secret terrorist group in Sicily; originally opposed tyranny but evolved into a criminal organization in the middle of the 19th century