individuality

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

• noun The aggregate of qualities and characteristics that distinguish one person or thing from others; character.
• noun An individual or distinguishing feature.
• noun The quality or state of being individual; singularity.
• noun A single, distinct entity.
• noun Archaic Indivisibility.

from The Century Dictionary.

• noun The condition or mode of being individual.
• noun The particular or distinctive character of an individual; that quality, or aggregate of qualities, which distinguishes one person or thing from another; idiosyncrasy: as, a person of marked individuality.
• noun A personality; a personage; an individual.
• noun The existence, efforts, interests, or concerns of the individual as distinguished from the interests or concerns of the community.
• noun In biology:
• noun Physiological completeness or independence; the ability of an organism to perform its normal functions or live out its life without the cooperation of others.
• noun Structural independence, or homology with or morphological equivalence to a physiological individual.
• noun The uniqueness of a living being, or its difference from others of its kind and from the rest of nature. It is in this sense that the offspring is said to inherit the individuality or constitution of a parent.

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

• noun The quality or state of being individual or constituting an individual; separate or distinct existence; oneness; unity.
• noun The character or property appropriate or peculiar to an individual; that quality which distinguishes one person or thing from another; the sum of characteristic traits; distinctive character.
• noun A habit of thinking and acting in one's own distinctive manner and as one believes appropriate, not being heavily influenced by the opinions of others; -- of people.

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

• noun uncountable The characteristics which contribute to the differentiation or distinction of someone or something from a group of otherwise comparable identity.
• noun countable A person.

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

• noun the distinct personality of an individual regarded as a persisting entity
• noun the quality of being individual