(Greek > Latin: a suffix; one who believes in; one who is engaged in; someone who does something)

seditionist (s) (noun), seditionists (pl)
A person, or people, who strive to incite people to rebel against the authority of a state or monarch: "The man's speech to the group was enough to label him as a seditionist and it also resulted in his arrest by government agents."
segregationist (s) (noun), segregationists (pl)
Someone or those who separate or disconnect people or things from others: In the past, there were U.S. policies when government segregationists kept Indian nations isolated on their reservations.
A specialist in the science of earthquakes and their effects.
Someone who is skilled in selenography (descriptions of the physical features of the moon).
Anyone who studies the nature and history of the moon.
Someone who manages or operates a semaphore.
Someone who studies the branch of linguistics that deals with the study of meaning, changes in meaning, and the principles that govern the relationship between sentences, images, or words and their meanings.
sensualist (s) (noun), sensualists (pl)
A person who likes, pursues, or indulges too much in the pleasures of life: Sharon was a sensualist who often spent time in the whirlpool bath because it was such a wonderful feeling for her to be there.
serendipitist (s) (noun), serendipitists (pl)
Someone who makes happy and unexpected discoveries unintentionally.
Someone who uses the method of musical composition in which all twelve chromatic tones of the octave appear in strict order.
Someone who is involved with the production of raw silk and the rearing of silkworms for the purpose of producing silk.
Someone who is involved in sericulture or who grows silk-worms for the production of silk.