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

A secrecy of cryptologists.
cultist (s) (noun), cultists 9PL0
A member of a cult.
Someone who studies dogs and who is concerned with canine evolution, breed development and differentiation, canine behavior and training, and canine history.
A physician, usually skilled in anatomical pathology, who is especially trained and experienced in cytopathology or disease changes within individual cells or cell types.
Someone who is a specialist in the art of engraving gems for finger rings.
Someone who specializes in the identification by comparison of fingerprints; and also, who deals with the classifications of fingerprints.
Anyone who favors, or is involved with, the deletion of a given passage or work.
deltiologist (s) (noun), deltiologists (pl)
Someone who collects post cards. There is no connection to the "deltic muscle".
Someone who writes about, or is versed in, demonology.
A specialist in dating by examining tree rings.
A specialist in the identification and classification of trees and shrubs.
denialist (s) (noun), denialists (pl)
1. Someone who denies an assertion in a controversial political debate or relating to denial in a controversial political debate.
2. Anyone who increasingly has come to maintain personal beliefs even in the face of solid scientific evidence.

It refers to people who deny a range of issues from childhood vaccines to genetically modified foods in which a person increasingly has come to maintain personal denials even in the face of solid scientific evidence.

Someone who speaks through clenched teeth.