To Roman grammarians there were two kinds of nouns (Latin nomen, nomina, 'name; noun'): substantives (nomina substantiva) and adjectives (nomina adjectiva). Later English grammarians basically split the category of nomen into substantives (later called simply nouns) and adjectives. The distinction in Roman grammar had to do with nouns adjective being declined in the same manner as nouns substantive. Of course, it is interesting to note that both substantive and adjective started our as adjectives.

Ceci n'est pas un seing.