-an words are initially nouns that have come to be used as adjectives, while -ish words are only adjectives. The English language readily makes adjectives from

-an words are initially nouns that have come to be used as adjectives, while -ish words are only adjectives. The English language readily makes adjectives from nouns, but not the other way round. Nominalized adjectives are used for collective groups at most (which is why you can say "the French") but rarely become regular nouns.