id

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

• noun In Freudian theory, the division of the psyche that is totally unconscious and serves as the source of instinctual impulses and demands for immediate satisfaction of primitive needs.

from The Century Dictionary.

• An abbreviation of idem.
• A common termination in adjectives (and nouns derived from adjectives) of Latin origin, as in acid, arid, fluid, vivid, turbid, morbid, flaccid, frigid, torrid, solid, etc. It is not used as a formative in English.
• [NL. -idum, neut. of L. -idus.] In chem., a formative (also spelled -ide, and when so spelled generally pronounced -īd) suffixed to names of elements to form names of compounds, as in oxid, chlorid, bromide, iodide, sulphid, etc., designating compounds of oxygen, chlorin, bromine, iodine, sulphur, etc.
• The termination of nouns Englished from Latin or New Latin feminine nouns (ultimately Greek or on the Greek model) in -is, as caryatid, hydatid, etc.
• In zoology, the termination of nouns Englished from Latin or New Latiu nouns in -idæ, as felid, from Felidæ, fringillid, from Fringillidæ, etc.
• noun In Weismann's doctrine of germ-plasm, the substance of inheritance or the bearer , in the germ-plasm, of the hereditary qualities of a single complete organism, or
• noun in the somatic idioplasm of the hereditary qualities of a group of cells or a part of a developing embryo or growing organism.
• noun This termination affords a simple and regular method of transforming a family name ending in -idæ into a common ‘English’ noun serving as a name for any member of the family. Thus, any member of the Felidæ is a felid, any of the Bradypodidæ a bradypodid, any of the Gadidæ a gadid, etc. This overcomes the ambiguity of using the popular name of some member of the family as a common name for all. The popular name is often not conterminous in meaning with the New Latin name and it always has a set of cross associations that are absent from the New Latin name. The two kinds of names do not cover the same ground. Every member of the Bradypodidæ is a sloth, but not every member of the Gadidæ is a cod, as several other well-known fishes, such as the pollack and haddock, are members of that family.
• noun A termination used by Osborn to designate the cusps of the lower teeth: for example, the cusp on a lower molar that corresponds to the hypocone of an upper tooth is the hypoconid, etc.

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

• noun any document testifying to teh identity of the bearer, especially a card or badge.
• noun (Zoöl.) A small fresh-water cyprinoid fish (Leuciscus idus or Idus idus) of Europe. A domesticated variety, colored like the goldfish, is called orfe in Germany.
• noun (Psychoanalysis) That part of a person's psyche which is the unconscious source of impulses seeking gratification or pleasure; the impulses are usually modified by the ego and superego before being acted upon.

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

• noun informal A Roman numeral representing four hundred and ninety-nine (499).
• noun The unconscious impulsive component of the personality in the Freudian psychoanalytic model.
• noun Alternative spelling of ide.
• noun computing identifier
• noun Used in citations to state that the citation is to the work immediately previously cited.

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

• noun a card or badge used to identify the bearer
• noun a state in the Rocky Mountains
• noun (psychoanalysis) primitive instincts and energies underlying all psychic activity