We found 18 dictionaries that define the word mountains:

General (13 matching dictionaries)

1. mountains: Merriam-Webster.com
2. mountains: Oxford Learner's Dictionaries
3. mountains: Collins English Dictionary
4. mountains: Vocabulary.com
5. Mountain's, Mountains, mountain's, mountains, mountains: Wordnik
6. Mountains, mountains: Cambridge Advanced Learner's Dictionary
7. Mountains, mountains: Wiktionary
8. mountains: Dictionary.com
9. mountains: Cambridge Essential American English Dictionary
10. Mountains (Biffy Clyro song), Mountains (EP), Mountains (LSD song), Mountains (Lonestar album), Mountains (Lonestar song), Mountains (Prince song), Mountains (Steamhammer album), Mountains (band), Mountains, The Mountains: Wikipedia, the Free Encyclopedia
11. Mountains: E Cobham Brewer, The Reader's Handbook
12. Mountains: Dictionary/thesaurus
13. mountains: Wikimedia Commons US English Pronunciations

Computing (1 matching dictionary)

14. Mountains: Encyclopedia

Medicine (1 matching dictionary)

15. Mountains: Medical dictionary

Miscellaneous (2 matching dictionaries)

16. Brilliant Dream Dictionary (No longer online)
17. Mountains: Idioms

Slang (1 matching dictionary)

18. mountains: Urban Dictionary

(Note: See mountain as well.)

Definitions from Wiktionary (mountains) ▸ noun:  mountain range Similar: mount, highland, upland, Hills, valley, Foothills, mountaintop, mountainside, vallies, mountainous, more... Opposite: valleys, plains, depressions, basins, lowlands Types: Rocky Mountains, AppalachiMountains, Andes Mountains, HimalayMountains, Swiss Alps, more... Phrases: Rocky Mountains, Blue Mountains, white mountains, Appalachian Mountains, smoky mountains, more... Adjectives: high, lofty, distant, rugged, western, southern, northern, blue, steep, snowy, low Colors:     gray,     charcoal,     stone,     silver,     pewter, more... ▸ Words similar to mountains ▸ Usage examples for mountains ▸ Idioms related to mountains ▸ Wikipedia articles (New!) ▸ Popular adjectives describing mountains ▸ Words that often appear near mountains ▸ Rhymes of mountains ▸ Invented words related to mountains