We found 15 dictionaries that define the word by the bye:

General (11 matching dictionaries)

1. by the bye: Merriam-Webster
2. by the bye: Collins English Dictionary
3. by the bye: Vocabulary.com
4. by the bye: Wordnik
5. by the bye: Wiktionary
6. By the bye, by the bye: Dictionary.com
7. by the bye: Rhymezone
8. BY THE BYE: Dictionary of Americanisms (1848)
9. by the bye: FreeDictionary.org
10. by the bye: Mnemonic Dictionary
11. by the bye: TheFreeDictionary.com

Business (3 matching dictionaries)

12. Bouvier's Law Dictionary 1856 Edition (No longer online)
13. By the bye: Legal dictionary
14. by the bye: Financial dictionary

Computing (1 matching dictionary)

15. by the bye: Encyclopedia

Definitions from WordNet (by the bye) ▸ adverb:  introducing a different topic Opposite: by way, incidentally, as aside ▸ Words similar to by the bye ▸ Usage examples for by the bye ▸ Idioms related to by the bye ▸ Wikipedia articles (New!) ▸ Words that often appear near by the bye ▸ Rhymes of by the bye ▸ Invented words related to by the bye