aura

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun An invisible emanation or field of energy believed to radiate from a person or object.
• noun A distinctive but intangible quality that seems to surround a person or thing; an atmosphere.
• noun Medicine A sensation, as of a cold breeze or a bright light, that precedes the onset of certain disorders, such as an epileptic seizure or an attack of migraine.

from The Century Dictionary.

• noun An old native name of any South American vulture excepting the condor; an urubu, tzopilotl, gallinazo, turkey-buzzard, or carrion-crow.
• noun [capitalized] In Greek myth, a personification of the lighter winds or breezes, the divinities of the air.
• noun A supposed influence, force, or imponderable matter proceeding from a body and surrounding it as an atmosphere; specifically, an imponderable substance supposed to emanate from all living things, to consist of the subtle essence of the individual, and to be a means of manifesting what is called animal magnetism, and also a medium for the operation of alleged mesmeric, clairvoyant, and somnambulic powers. Also called nerve-aura, or nervaura.
• noun Figuratively, atmosphere; air; character, etc.
• noun A peculiar sensation resembling that produced by a current of air. See epileptic aura, below.

from the GNU version of the Collaborative International Dictionary of English.

• noun Any subtile, invisible emanation, effluvium, or exhalation from a substance, as the aroma of flowers, the odor of the blood, a supposed fertilizing emanation from the pollen of flowers, etc.
• noun (Med.) The peculiar sensation, as of a light vapor, or cold air, rising from the trunk or limbs towards the head, a premonitory symptom of epilepsy or hysterics.
• noun a supposed electric fluid, emanating from an electrified body, and forming a mass surrounding it, called the electric atmosphere. See Atmosphere, 2.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun Distinctive atmosphere or quality associated with something.
• noun An invisible force surrounding a living creature.
• noun medicine Perceptual disturbance experienced by some migraine sufferers before a migraine headache.
• noun medicine Telltale sensation experienced by some people with epilepsy before a seizure.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a sensation (as of a cold breeze or bright light) that precedes the onset of certain disorders such as a migraine attack or epileptic seizure
• noun a distinctive but intangible quality surrounding a person or thing
• noun an indication of radiant light drawn around the head of a saint