| Part of speech | common noun |
|---|---|
| Hyphenation | te·o·ri·o |
| Singular | Plural | |
|---|---|---|
| Nominative | teorio | teorioj |
| Accusative | teorion | teoriojn |
| Afrikaans | teorie |
|---|---|
| Catalan | teoria |
| Czech | teorie; theorie |
| Danish | teori |
| Dutch | theorie |
| English | theory |
| Faeroese | ástøði |
| French | théorie |
| German | Theorie |
| Greek | θεωρία |
| Latin | ars |
| Low German | teory |
| Malay | teori |
| Portuguese | teoria |
| Saterland Frisian | Theorie |
| Spanish | teoría |
| Swedish | teori |
| Welsh | damcaniaeth |
| West Frisian | teory |