We found 8 dictionaries that define the word mares' tails:

General (5 matching dictionaries)

1. mare's tails, mares' tails: Merriam-Webster
2. mare's tails: Oxford Learner's Dictionaries
3. mare's-tails, mare's tails, mares'-tails, mares' tails: Wiktionary
4. mare's-tails, mares'-tails: Dictionary.com
5. mare's-tails, mares'-tails: TheFreeDictionary.com

Computing (1 matching dictionary)

6. mare's-tails: Encyclopedia

Sports (1 matching dictionary)

7. Mare's tails: Sports Definitions

Tech (1 matching dictionary)

8. Glossary of Meteorology (No longer online)

Definitions from Wiktionary (mares' tails) ▸ noun:  A cirrus cloud formation resembling horse tails. ▸ Words similar to mares' tails ▸ Usage examples for mares' tails ▸ Idioms related to mares' tails ▸ Wikipedia articles (New!) ▸ Words that often appear near mares' tails ▸ Rhymes of mares' tails ▸ Invented words related to mares' tails