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

A specialist in hippology or the study of horses.
Anyone who eats the meat of horses as a source of food.
A specialist in hippotomy or the anatomy and/or dissection of horses.
Someone who cultivates leeches for biological studies or for medical applications.
histologist, microanatomist
1. A scientist who studies tissues and cells by using microscopic techniques.
2. A specialist in the study of cells and microscopic tissues.
historical geologist (s) (noun), historical geologists (pl)
A geologists who divides all time since the formation of the earliest known rocks (about four billion years ago) into four major divisions: Precambrian, Paleozoic, Mesozoic, and Cenozoic eras: A historical geologis maintains that each era, except the Cenozoic, ended with profound changes in the disposition of the Earth's continents and mountains and was characterized by the emergence of new forms of life.

Broad cyclical patterns, which run through all historical geology, include a period of mountain and continent building followed by one of erosion, and then by a new period of elevation.

A medical practitioner of homeopathy.
1. Someone who prepares homilies.
2. Anyone who preaches to a congregation.
homunculophilist (s) (noun), homunculophilists (pl)
A collector of figurines: Mrs. Roberts loved little statuettes and had quite a number of them, all placed decoratively in her living room. Her neighbours thought she was a homunculophilist because she bought even more each time she went on vacation!
horologist (s) (noun), horologists (pl)
Someone who studies the science of measuring time: Not only did Tom take courses about how clocks worked, but he also became an excellent horologist and was very skilled in making clocks, watches, and even sundials.
horticulturist (s) (noun), horticulturists (pl)
Someone who strives to improve crop yields, quality, nutritional value, and resistance to insects, diseases, and environmental stresses: Horticulturists work in plant propagation, crop production, plant breeding and genetic engineering, plant biochemistry, plant physiology, and the storage, processing, and transportation of fruits, berries, nuts, vegetables, flowers, trees, shrubs, etc.
humorist (s), humorists (pl) (nouns)
1. Someone who acts, speaks, or writes in an amusing way; such as, a comedian.
2. Anyone known to be amusing and to have a quick wit.
3. A person who writes, or performs, comic material.
1. Someone who is skilled in hydrology.
2. A practitioner of hydrology who works within the fields of either earth or environmental science, or civil and environmental engineering.