What is "proper adjective"

n. (context grammar English) An adjective derived from a proper noun, such as ''British'' derived from ''Britain''.

In English orthography, the term proper adjective is sometimes applied to adjectives that take initial capital letters, and the term common adjective to those that do not. These terms are used informally only; they are not used by grammarians or linguists. For example, a person from Boston is Bostonian. Bostonian is a proper adjective.