Demonym

A demonym or gentilic is a word used for people or the inhabitants of a place. The name of a people's language is usually the same as this word, for example, the "English" (language or people). Some places may not have a word for the people that live there.
Suffix demonyms
The English language has many ways to create demonyms. The most common is to add a suffix to the end of the location's name. These may use Latin, Semitic or Germanic suffixes, such as:
-an (America - American, Rome - Roman)
-ian (Paris - Parisian, Russia - Russian, India - Indian, Canada - Canadian)
-ine (Florence - Florentine, Argentina - Argentine)
-ite (Vancouver - Vancouverite, Moscow - Muscovite) (mostly cities)
-er (New Zealand - New Zealander, London - Londoner) (mostly cities)
-eno (Los Angeles - Angeleno or Los Angeleno, uses the Spanish eno suffix for demonyms)
-ish (Spain - Spanish, Denmark - Danish) (mostly countries)
"-ish" is usually used as an adjective. Many common "-ish" forms have different demonyms. (Spain/Spanish/Spaniard; Denmark/Danish/Dane; Judea/Jewish/Jew or Judean; Poland/Polish/Pole)
-ese (Taiwan - Taiwanese, Vienna - Viennese, Tyrol - Tyrolese, Vietnam - Vietnamese, Japan - Japanese)
"-ese" is usually only proper as an adjective, or to refer to the entire group of people. For example, "The Chinese" means all people from China.
-i (Iraq - Iraqi, Bengal - Bengali) (mostly Middle Eastern and South Asian places)
-ic (Hispania - Hispanic)
"-ic" is mostly used as an adjective to refer to an ethnic or linguistic group, for example Hispanic vs. Spanish
-iote (Cyprus - Cypriote, Phanar - Phanariote), especially for Greek locations.
Irregular forms
In many cases, both the location's name and the demonym are created by using a suffix, for example England and English and Englishman. This is not always true, for example, France - French; Philippines - Filipino or Pilipino.
In a few cases, the name of the country is not at all related to the name of the people (Netherlands - Dutch). This is usually because the two words come from different languages. The demonyms in federal states or autonomous region can also differ in this way. For example, people in Khatumo State are often called reer darawiish. That's because the dominant tribe Dhulbahante used to be anti-colonial dervishes.Reer DarawiishDemonyms can be nouns or adjectives. In many cases the noun and adjective forms are the same (Canadian/Canadian); in other cases they are different (Spaniard/Spanish).
In the case of Canadian provinces and territories and U.S. states, demonyms are not usually used as adjectives.
Cultural problems
Some peoples, mainly cultures that were taken over by European colonists, have no demonym. They may also have a demonym that is the same as the name of their nation. Examples include Iroquois, Aztec, Maori, and Czech. Often, the native languages of these people have forms that did not get used in English. In Czech, for example, the language is Cestina, the nation is Cesko or Ceska republika, and the people are Cesi.
The demonym for people of the United States of America has a similar problem. "American" can mean either someone from the United States, or someone from any part of American region or the two American continents (North America and South America). United Statian is not frequently used in English, but it exists. It is commonly used in Spanish (estadounidense) and widely used in Latin American Spanish. French (etatsunien(ne)) exists but is rarely used, Portuguese (estado-unidense or estadunidense) but it is not as commonly used, Italian (statunitense) exists but is rarely used, and also in Interlingua (statounitese). In Esperanto the country is Usono and the demonym is Usonano, avoiding confusion with Amerikano. US American (for the noun) and US-American can be used but is not widely used in German (US-Amerikaner'').