The suffix “-ology” means the study of something, and the suffix “-onomy” means the laws or arrangement of something. Both come from Greek, and science uses them to name whole fields of knowledge.
Scientists build most field names from two pieces: a Greek or Latin root for the subject, and an ending that says what kind of knowledge it is. Once you know a handful of roots and these two endings, you can guess what a new science word means before you look it up.
What does “-ology” mean?
“-Ology” means the study of a subject, and it comes from the Greek word logos, meaning “word” or “reason” (Merriam-Webster).
Attach it to a root and you name a whole branch of science. Bio- means life, so biology is the study of living things. Geo- means Earth, so geology is the study of Earth’s rocks and structure. This page covers the suffix and a set of common examples. It does not cover every English word that ends in “-ology,” since some, like “apology,” are not science words at all.
What does “-onomy” mean?
“-Onomy” means the laws or ordered system governing a subject, and it comes from the Greek word nomos, meaning “law” or “custom” (Merriam-Webster).
Astronomy is the study of the laws that govern stars, planets and space. Taxonomy is the system of rules for sorting living things into groups. This suffix is rarer in science than “-ology,” and this page only covers the handful of science terms that use it, not everyday words like “economy” or “gastronomy.”
What are common -ology and -onomy words in science?
The table below lists 24 science fields named with these two suffixes, from biology to taxonomy.
| Term | What it studies |
|---|---|
| Biology | Living things and how they work |
| Geology | Earth’s rocks, layers and history |
| Ichthyology | Fish |
| Entomology | Insects |
| Herpetology | Reptiles and amphibians |
| Ornithology | Birds |
| Arachnology | Spiders and their relatives |
| Mycology | Fungi, including mushrooms and molds |
| Zoology | Animals in general |
| Meteorology | Weather and the atmosphere |
| Paleontology | Fossils and prehistoric life |
| Volcanology | Volcanoes and how they erupt |
| Seismology | Earthquakes and how the ground shakes |
| Anthropology | Human societies and cultures |
| Archaeology | Human history uncovered through excavated objects |
| Physiology | How the bodies of living things function |
| Psychology | The mind and behavior |
| Virology | Viruses |
| Immunology | How the body defends itself from disease |
| Climatology | Climate patterns over long periods of time |
| Mineralogy | Minerals and crystals |
| Ecology | How living things interact with each other and their environment |
| Astronomy | Stars, planets and the rest of space |
| Taxonomy | Sorting living things into ordered groups |
| Agronomy | Soil, farmland and crop production |
This table covers a working set of terms for a classroom or homeschool lesson. It is not a full list of every science field name, and many narrower specialties exist inside each one.
How do you figure out a new “-ology” or “-onomy” word?
Break the word into its root and its ending, then translate each piece separately. A word you have never seen, like “cardiology,” splits into cardio- (heart) and -ology (study of), so it means the study of the heart.
Try it with the words in the table above. Biology splits into bio- (life) and -ology. Geology splits into geo- (earth) and -ology. This method works for guessing new words, but it will not tell you the fine details of a field, such as which animals a zoologist specializes in. For that you need to check a classification guide or a dictionary.
Where can you learn more about a specific field?
Start with LearningHaven’s own science section for lessons on many of the fields listed above, and the vocabulary section for more work on roots, prefixes and suffixes.
For a hands-on introduction built for kids, the American Museum of Natural History runs OLogy, a science site organized by field, from paleontology to marine biology (American Museum of Natural History). This page does not attempt to summarize every field OLogy covers. It is a starting point, not a substitute for exploring the site itself.
Ology and onomy quiz
Match each term to what it studies. Write your answers, then check them below.
- Ichthyology
- Entomology
- Astronomy
- Taxonomy
- Volcanology
- Ornithology
Choices: birds · classifying living things · fish · insects · stars and planets · volcanoes
Show answers and reasoning
- Ichthyology – fish. Root ichthy- means fish.
- Entomology – insects. Root entomo- means insect.
- Astronomy – stars and planets. Root astro- means star.
- Taxonomy – classifying living things. Root taxo- means arrangement.
- Volcanology – volcanoes. Root is the word “volcano” itself.
- Ornithology – birds. Root ornith- means bird.