We found 27 dictionaries that define the word one on one:

General (20 matching dictionaries)

1. one on one: Longman Dictionary of Contemporary English
2. one-on-one: Merriam-Webster
3. one-on-one, one-on-one: Oxford Learner's Dictionaries
4. one-on-one: American Heritage Dictionary of the English Language
5. one-on-one, one-on-one, one on one: Collins English Dictionary
6. one-on-one: Vocabulary.com
7. one on one: Wordnik
8. one-on-one: Cambridge Advanced Learner's Dictionary
9. one-on-one, one on one: Wiktionary
10. one-on-one: Webster's New World College Dictionary, 4th Ed.
11. one-on-one: Infoplease Dictionary
12. one-on-one, one on one: Dictionary.com
13. one-on-one: Cambridge Essential American English Dictionary
14. One on One (Cheap Trick album), One on One (Hall & Oates song), One on One (Mira Calix album), One on One (Steve Camp album), One on One (TV series), One on One (novel), One on One (song), One on One (soundtrack), One on One (tour), One on One, One-on-one, One on one: Wikipedia, the Free Encyclopedia
15. one-on-one: Rhymezone
16. one-on-one, one on one: FreeDictionary.org
17. one-on-one: Mnemonic Dictionary
18. one-on-one, one on one: TheFreeDictionary.com

Art (1 matching dictionary)

19. ODLIS: Online Dictionary of Library and Information Science (No longer online)

Computing (1 matching dictionary)

20. one-on-one: Encyclopedia

Slang (2 matching dictionaries)

21. American-Australian Slang Dictionary (No longer online)
22. one on one: Urban Dictionary

Sports (3 matching dictionaries)

23. Hickok Sports Glossaries (No longer online)
24. Texas Hold'em Dictionary (No longer online)
25. One-on-one: Sports Definitions

Definitions from Wiktionary (One on one) ▸ adjective:  Alternative form of one-on-one [(chiefly Canada, US) Involving direct communication or competition between two people.] Similar: person-to-person, private, man-to-man, individual, mano-a-mano, singlehanded, single handed, onehanded, head on, oneshot, more... Opposite: group, team, collective, multiple, mass Phrases: go one on one, one on one specialist, one on one battle, more... Adjectives: engaged, rite, open door, trial, upstage, lead, go, on the move, stand-up, head-on ▸ Words similar to one on one ▸ Usage examples for one on one ▸ Idioms related to one on one ▸ Wikipedia articles (New!) ▸ Popular nouns described by one on one ▸ Words that often appear near one on one ▸ Rhymes of one on one ▸ Invented words related to one on one