Even though people from each state of the U.S.A have their own names, if you wanted to know the nationality 'American', in Spanish you would use <em>estadounidense. </em>
Silvia es estadounidense.
Todos nosotros somos estadounidenses.
Most adjectives agree in gender and number with the noun or pronoun that they modify, so these changes also apply when using the 'opposite' adjectives. An exception to this rule are the adjectives that do not change and in Spanish are called 'invariable'.
An example of this is the adjective precoz meaning immature or premature.
