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Meaning of cluster headache

clus'ter head"ache

Pronunciation: [key]
— Pathol. Pathol.
  1. a type of severe recurrent headache associated with dilated carotid arteries and the release of histamine, characterized by sudden attacks of intense pain behind the nostril and eye on one side and accompanied by runny nose, tearing, and flushed skin.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.