Noun
A name for an inhabitant or native of a specific place, usually derived from the name of the place.
Why is it that people from the United States use American as their demonym?
(obsolete) A pseudonym formed of an adjective.
The Logophile has my favourite demonym; I would write under it if he didn't.
Just under 40% of the population of The Hague regularly attends a house of worship. citation The demonym of The Hague officially is Hagenaar, but the term Hagenees is informally used for someone who was born and grew up in The Hague. Source: Internet
In the case of most nationalities, however, the plural of the demonym noun is used for this purpose: (the) Americans, (the) Poles. Source: Internet