We found 8 dictionaries that define the word cluster headaches:

General (4 matching dictionaries)

1. cluster headaches: Merriam-Webster
2. cluster headaches: Wiktionary
3. Cluster headaches: Wikipedia, the Free Encyclopedia
4. Cluster Headaches: TheFreeDictionary.com

Computing (1 matching dictionary)

5. Cluster Headaches: Encyclopedia

Medicine (3 matching dictionaries)

6. cluster headaches: Merriam-Webster Medical Dictionary
7. Cluster Headaches: Medical dictionary
8. University of Maryland Glossary of Medical Terms (No longer online)

(Note: See cluster_headache as well.)

Definitions from Wiktionary (cluster headache) ▸ noun:  (pathology) An extremely painful, cyclical and unilateral headache. ▸ Also see cluster_headache ▸ Words similar to cluster headaches ▸ Usage examples for cluster headaches ▸ Idioms related to cluster headaches ▸ Wikipedia articles (New!) ▸ Words that often appear near cluster headaches ▸ Rhymes of cluster headaches ▸ Invented words related to cluster headaches