genius

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

• noun Extraordinary intellectual and creative power.
• noun A person of extraordinary intellect and talent.
• noun A person who has an exceptionally high intelligence quotient, typically above 140.
• noun A strong natural talent, aptitude, or inclination.
• noun One who has such a talent or inclination.
• noun The prevailing spirit or distinctive character, as of a place, a person, or an era.
• noun Roman Mythology A tutelary deity or guardian spirit of a person or place.

from The Century Dictionary.

• noun The ruling or predominant spirit of a place, person, or thing; the power, principle, or influence that determines character, conduct, or destiny (supposed by the ancients to be a tutelar divinity, a good spirit, or an evil demon, usually striving with an opposing spirit for the mastery); that which controls, guides, or aids: as, my good genius came to the rescue; his evil genius enticed him.
• noun A disembodied spirit regarded as affecting human beings in certain ways, but not as connected with any one individually.
• noun A type or symbol; a concrete representative, as of an influence or a characteristic; a generic exemplification.
• noun Prevailing spirit or inclination; distinguishing proclivity, bent, or tendency, as of a person, place, time, institution, etc.; special aptitude or intellectual quality; intrinsic characteristic or qualification: as, a genius for poetry, or for diplomacy; the genius of Christianity, of the Elizabethan period, of the American Constitution, of the Vatican.
• noun Exalted mental power distinguished by instinctive aptitude, and independent of tuition; phenomenal capability, derived from inspiration or exaltation, for intellectual creation or expression; that constitution of mind or perfection of faculties which enables a person to excel others in mental perception, comprehension, discrimination, and expression, especially in literature, art, and science.
• noun A person having such mental power; a person of general or special intellectual faculties developed in a phenomenal degree.

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

• noun A good or evil spirit, or demon, supposed by the ancients to preside over a man's destiny in life; a tutelary deity; a supernatural being; a spirit, good or bad. Cf. jinnee.
• noun The peculiar structure of mind with which each individual is endowed by nature; that disposition or aptitude of mind which is peculiar to each man, and which qualifies him for certain kinds of action or special success in any pursuit; special taste, inclination, or disposition.
• noun Peculiar character; animating spirit, as of a nation, a religion, a language.
• noun Distinguished mental superiority; uncommon intellectual power; especially, superior power of invention or origination of any kind, or of forming new combinations.
• noun A man endowed with uncommon vigor of mind; a man of superior intellectual faculties and creativity.
• noun the genius or presiding divinity of a place; hence, the pervading spirit of a place or institution, as of a college, etc.

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

• noun Someone possessing extraordinary intelligence or skill; especially somebody who has demonstrated this by a creative or original work in science, music, art etc.
• noun Extraordinary mental capacity.
• noun inspiration, a mental leap, an extraordinary creative process.
• noun Roman mythology The guardian spirit of a place or person.
• noun A way of thinking, optimizing one's capacity for learning and understanding.

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

• noun a natural talent
• noun someone who is dazzlingly skilled in any field
• noun exceptional creative ability
• noun unusual mental ability
• noun someone who has exceptional intellectual ability and originality