We found 26 dictionaries that define the word run of the mill:

General (21 matching dictionaries)

1. run of the mill: Longman Dictionary of Contemporary English
2. run-of-the-mill: Merriam-Webster
3. run-of-the-mill: Oxford Learner's Dictionaries
4. run-of-the-mill: American Heritage Dictionary of the English Language
5. run-of-the-mill, run-of-the-mill, run of the mill: Collins English Dictionary
6. run-of-the-mill: Vocabulary.com
7. run-of-the-mill: Wordnik
8. run-of-the-mill: Cambridge Advanced Learner's Dictionary
9. run-of-the-mill, run of the mill: Wiktionary
10. run-of-the-mill: Webster's New World College Dictionary, 4th Ed.
11. run-of-the-mill: Infoplease Dictionary
12. run-of-the-mill, run of the mill: Dictionary.com
13. run-of-the-mill: Online Etymology Dictionary
14. Run of the Mill (George Harrison song), Run of the Mill (Judas Priest song): Wikipedia, the Free Encyclopedia
15. run-of-the-mill: Rhymezone
16. run-of-the-mill, the run of the mill: FreeDictionary.org
17. run-of-the-mill: Mnemonic Dictionary
18. run-of-the-mill: TheFreeDictionary.com
19. Run of the mill: World Wide Words

Business (1 matching dictionary)

20. run of the mill: Legal dictionary

Computing (1 matching dictionary)

21. run-of-the-mill: Encyclopedia

Miscellaneous (1 matching dictionary)

22. run-of-the-mill: Idioms

Slang (2 matching dictionaries)

23. run of the mill: English slang and colloquialisms used in the United Kingdom
24. run of the mill: Urban Dictionary

Definitions from Wiktionary (Run of the mill) ▸ adjective:  Alternative spelling of run-of-the-mill [(figurative) Ordinary; not special.] Similar: ordinary, unexceptional, run-of-the-mine, run-o'-the-mill, run o' the mill, cliched, runthrough, work-a-day, ho hum, lame-stream, more... Opposite: extraordinary, unusual, rare, unique Phrases: opposite of run of the mill, more... Adjectives: garden variety, trivial, workaday, conventional, run-of-the-mill, commonplace, basic, everyday, ordinary, popular ▸ Word origin ▸ Words similar to run of the mill ▸ Usage examples for run of the mill ▸ Idioms related to run of the mill ▸ Wikipedia articles (New!) ▸ Popular nouns described by run of the mill ▸ Words that often appear near run of the mill ▸ Rhymes of run of the mill ▸ Invented words related to run of the mill