-ists1) SUFFIX -ist is used in place of -ism to form count nouns and adjectives. The nouns refer to people who have particular beliefs. The adjectives describe something related to or based on particular beliefs.
Later he was to become famous as a pacifist.
...fascist organisations.2) SUFFIX -ist is used to form count nouns referring to people who do a particular kind of work.
Susi Arnott is a biologist.3) SUFFIX -ist is added to nouns referring to musical instruments, in order to form nouns that refer to people who play these instruments.
...Hungarian pianist Christina Kiss.
English dictionary. 2008.