1. A recurrent, throbbing, very painful headache, often affecting one side of the head and sometimes accompanied by vomiting or by distinct warning signs, including visual disturbances.
2. Usually consisting of periodic attacks of headaches on one or both sides of the head that may be accompanied by nausea, vomiting, increased sensitivity of the eyes to light (photophobia), increased sensitivity to sound (phonophobia), dizziness, blurred vision, cognitive disturbances, and other symptoms.

Attacks are preceded by constriction of the cranial arteries, usually with the resultant prodromal sensory (especially ocular) symptoms and commence with the vasodilation that follows.

Not all severe headaches are migraines and not all migraines are severe.

Some factors known to make migraines worse in some patients include stress, food sensitivities, menstruation, and the onset of menopause.

Most patients will feel better if they lie down and avoid bright lights.

3. Etymology: from 1373, megrim, from Old French migraigne, from a vulgar pronunciation of Late Latin hemicrania, "pain in one side of the head, headache"; from Greek hemikrania, from hemi-, "half" + kranion, "skull".

The Middle English form was re-spelled in 1777 based on the French model.