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

desegregationist (s) (noun), desegregationists (pl)
Someone who advocates, or enforces, the opening of places and organizations to people of all races, genders, and ethnic groups, etc.: Martin Luther King was well-known as a desegregationist and he was assassinated by someone who was opposed to Mr. King's fight for equality of all races.
deuteragonist (s) (noun), deuteragonists (pl)
The second actor or person in a drama as distinguished from the protagonist or leading character: In classical Greek dram, a deuteragonist had the secondary role, or the second most important role, next to the protagonist.
deviationist (s) (noun), deviationists (pl)
Someone who favors transferring power from a central government to smaller political units.
One who marries a second time; especially, after the death of the first spouse.
Someone who specializes in the study of dinosaurs.
A writer of dissertations.
disunionist (s) (noun), disunionists (pl)
In U.S. History, a secessionist during the period of the U.S. Civil War.
One who dogmatizes, who asserts or lays down particular dogmas; especially, one who positively asserts or imposes his own opinions; a dogmatic person.
domatologist (s) (noun), domatologists (pl)
1. A person who studies houses: Rose was very interested in all kinds of houses, like duplexes, farmhouses, lodges, mansions, etc., and decided to become a domatologist and later be able to give advice to people who wanted to buy such a dwelling.
2. A professional housekeeper: The elderly and frail Mrs. Grant decided to hire a domatologist to help her with keeping her house clean and tidy.
dosimetrist (s) (noun), dosimetrists (pl)
1. A person who performs medical dose measurements: "At the drug rehabilitation center, the nurse who was also the dosimetrist, carefully measured the medications administered to the residents."
2. In radiation therapy, a person trained to make radiation measurements and also performs treatment-planning calculations: "Sean's cousin was trained to become a dosimetrist at the medical college and now he is working at a radiation clinic."
A writer of plays; a playwright.