We found 18 dictionaries that define the word oni:

General (12 matching dictionaries)

1. ONI: Oxford Learner's Dictionaries
2. ONI: American Heritage Dictionary of the English Language
3. ONI: Vocabulary.com
4. ONI, Oni, oni: Wordnik
5. ONI, oni: Wiktionary
6. ONI: Infoplease Dictionary
7. ONI: Dictionary.com
8. ONI, Oni (Japanese folklore), Oni (Street Fighter), Oni (band), Oni (disambiguation), Oni (folklore), Oni (game), Oni (letter), Oni (mythology), Oni (video game), Oni: Wikipedia, the Free Encyclopedia
9. Oni: Rhymezone
10. oni: FreeDictionary.org
11. oni: Mnemonic Dictionary
12. ONI: TheFreeDictionary.com

Art (1 matching dictionary)

13. Oni: ANIME AND MANGA GLOSSARY

Miscellaneous (2 matching dictionaries)

14. ONI: Acronym Finder
15. AbbreviationZ (No longer online)

Religion (1 matching dictionary)

16. Basic Terms of Shinto (No longer online)

Slang (1 matching dictionary)

17. Oni: Urban Dictionary

Tech (1 matching dictionary)

18. DOD Dictionary of Military Terms: Joint Acronyms and Abbreviations (No longer online)

(Note: See onis as well.)

Definitions from Wiktionary (ONI) ▸ noun:  A Japanese evil spirit or demon. ▸ noun:  (US military) Initialism of Office of Naval Intelligence. Similar: ushioni, demon, akuma, obake, otkon, gaki, yokai, angel of death, Isonade, kakodaimon, more... Opposite: angel, good spirit, divine being Types: oni with one eye, oni with two eyes, oni with three eyes, oni with four eyes, oni with five eyes, more... Phrases: ben oni, cama oni, Oni Press, Miye Oni, Oni Logan, more... Adjectives: wicked, first, japanese, present, other, red, russian, late, early, new, second ▸ Words similar to oni ▸ Usage examples for oni ▸ Idioms related to oni ▸ Wikipedia articles (New!) ▸ Popular adjectives describing oni ▸ Words that often appear near oni ▸ Rhymes of oni ▸ Invented words related to oni