gangdom vs yakuza

gangdom and yakuza both are nouns.

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

As nouns, yakuza is a hyponym of gangdom; that is, yakuza is a word with a more specific, narrower meaning than gangdom:

gangdom: underworld organizations
yakuza: organized crime in Japan; an alliance of criminal organizations and illegal enterprises

Other hyponyms of gangdom include Maffia, Mafia, Sicilian Mafia, Black Hand, Camorra, crime syndicate, family, mob, syndicate.

gangdom (noun)	yakuza (noun)
underworld organizations	organized crime in Japan; an alliance of criminal organizations and illegal enterprises
	a Japanese gangster