We found 22 dictionaries that define the word longest:

General (15 matching dictionaries)

1. longest: Merriam-Webster
2. longest: Oxford Learner's Dictionaries
3. longest: Collins English Dictionary
4. longest: Vocabulary.com
5. Longest, longest: Wordnik
6. longest: Cambridge Advanced Learner's Dictionary
7. Longest, longest: Wiktionary
8. Longest, longest: Dictionary.com
9. longest: Cambridge Essential American English Dictionary
10. Longest: Wikipedia, the Free Encyclopedia
11. longest: Webster's 1828 Dictionary
12. longest: FreeDictionary.org
13. longest: Mnemonic Dictionary
14. longest: TheFreeDictionary.com
15. longest: Rhymezone

Business (3 matching dictionaries)

16. longest: Merriam-Webster Legal Dictionary
17. longest: Legal dictionary
18. longest: Financial dictionary

Computing (1 matching dictionary)

19. longest: Encyclopedia

Medicine (1 matching dictionary)

20. longest: Medical dictionary

Miscellaneous (1 matching dictionary)

21. longest: Idioms

Slang (1 matching dictionary)

22. longest: Urban Dictionary

(Note: See long as well.)

Definitions from Wiktionary (Longest) ▸ noun:  A surname. Similar: large, best, shorter, last, Longo, longe, bigger, Every, Beste, likely, more... Opposite: shortest, briefest, smallest, nearest, quickest Phrases: longest lasting, longest lived, longest term, Longest word in English, Longest recorded sniper kills, more... Colors:     red,     blue,     green,     yellow,     orange, more... ▸ Words similar to longest ▸ Usage examples for longest ▸ Idioms related to longest ▸ Wikipedia articles (New!) ▸ Popular adjectives describing longest ▸ Words that often appear near longest ▸ Rhymes of longest ▸ Invented words related to longest