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

A collector of marbles.
martyrologist (s) (noun), martyrologists (pl)
1. A writer of martyrology.
2. An historian of martyrs.
3. Someone who specializes in the accounts of the lives and manners of the deaths of martyrs.
4. A writer of or a specialist in martyrology.
1. A person who is markedly more concerned with material things than with spiritual, intellectual, or cultural values.
2. Someone who denies the existence of spiritual substances, and maintains that the soul of man is the result of a particular organization of matter in the body.
mazologist (s) (noun), mazologists (pl)
Someone who studies the animal class of Mammalia which refers to warm-blooded creatures that have body hair and feed milk to its young.
mazomantist (s) (noun), mazomantists (pl)
Someone who predicts the future while watching a baby nursing milk from his or her mother.
An opium eater or one who eats opium.
A person of mediocre talents or ability; sometimes a person who takes a middle course.
megistothermic, megistotherm, megistothermy
A plant requiring a very high temperature for growth.
meliorist, melioristic
A disputant who advocates reform with the belief that human society can improve and that people can aid in making it better for everyone.
A collector of bowling-club badges.
A collector of bookmarks.
Someone who has a strong or spellbinding appeal; a fascinating person.

When the members of an audience sit mesmerized by a speaker, their reactions do not take the form of dancing, sleeping, or falling into convulsions; however, if Franz Anton Mesmer were addressing the audience, such behavior could be expected.

Mesmer was a visionary 18th-century physician who believed cures could be effected by having patients do things such as sit with their feet in a fountain of magnetized water while holding cables attached to magnetized trees. Mesmer then came to believe that magnetic powers resided in himself, and during highly fashionable curative sessions in Paris he caused his patients to have reactions ranging from sleeping or dancing to convulsions.

These reactions were actually brought about by hypnotic powers that Mesmer was unaware of possessing. One of his pupils, named Puységur, then used the term mesmerism (first recorded in English in 1802) for Mesmer's practices. The related word mesmerize (first recorded in English in 1829), having shed its reference to the hypnotic doctor, lives on in the sense “to enthrall”.

—From information found in
The American Heritage® Dictionary of the English Language
A collector of metalwork.
metempsychosist (s) (noun), metempsychosists (pl)
Someone who believes that it is posible for psychic actions to take place from one mind to other minds.
One versed in the study of meteors.