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

patrist, patristic
One versed in the lives or writings of the Fathers of the Christian Church.
pedagogist (s) (noun), pedagogists (pl)
A specialist or teacher of children: After finishing school and college, Susan became a student teacher and then an official pedagogist in teaching German in the school in the neighbouring town.
pedobaptist, paedobaptist (s) (noun); pedobaptists; paedobaptists (pl)
A person who practices, adheres to, or advocates infant baptism: Mr. and Mrs. Jones wanted to have their good neighbor, a pedobaptist, to christen their little newborn baby.
pedodontist, pediadontist (s) (noun); pedodontists; pediadontists (pl)
A dentist who practices dentistry that deals with children's teeth: Dr. Small, Tim's pedodontist, told Tim to open up his mouth so he could check his teeth for any possible cavities.
pedologist, paidologist (s) (noun); pedologists; paidologists (pl)
A person who studies children and their behavior: Because Sally didn't seem to act her age, at home or in school, her parents took her to Dr. Moon, a pedologist, in order to find out possible disorders in her development.
A person skilled in pedorthics and practicing its application in individual cases.
pedotrophist (s) (noun) ,pedotrophists (pl)
A specialist who has the knowledge and is adept in rearing a child: A pedotrophist is skilled, possesses the ability and the know-how to bring up children properly.
pejorist (PEJ or rist)
Someone who believes that the conditions in the world are becoming worse; such as, with climatic changes; what is happening with economics and government policies; religious hypocrisy or pretense of virtue; internet fraud; military wars; terrorism in the name of religion; greed, public and private individuals; false accusations in politics; ego-centric, foul-mouthed, rabble-rousing (stirring up the passions or prejudices of the public) talk-show hosts (on radio, television, and at rallies) and their followers; company executives, politicians, and others who lie and commit fraudulent acts; etc., etc.
Someone who is skilled in the therapeutic uses of mud.
A therapist who applies mud for therapeutic purposes, commonly in the form of hot mud packs in conjunction with mineral spa therapy, or by beauticians for purported effects on the skin.
peltrophilist (s) (noun), peltrophilists (pl)
A collector of pewterware: Sam's wife, a peltrophilist, loved objects made of an alloy of tin, copper, and antimony, and she had a special shelf in her kitchen with tableware and other kitchen utensils made of such metal.
A physician who treats prisoners, as in a penitentiary.
penologist (s) (noun), penologists (pl)
Someone who studies or is an expert in the theory and practice of prison management: Tom's uncle was a penologist who was involved in the treatment of crime and the organisation in prisons.