(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.
pelopathist (s) (noun), pelopathists (pl)
Someone who is skilled in the therapeutic uses of mud: Mike's father was a pelopathist and worked in a spa where patients were treated with mudpack for those who wanted to improve their complexion.
pelotherapist (s) (noun), pelotherapists (pl)
A therapist who applies mud for therapeutic purposes: Alice was a pelotherapist who used hot mud packs in conjunction with mineral spa therapy and she also worked as a beautician using mud for improving one's 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.