id

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. 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.

Century Dictionary and Cyclopedia

1. An abbreviation of idem.
2. 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.
3. [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. Usage is, in general, in favor of the form -ide; but in new formations, and in many of the old ones, the form -id is also in use.
4. 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.
5. In zoology, the termination of nouns Englished from Latin or New Latiu nouns in -idæ, as felid, from Felidæ, fringillid, from Fringillidæ, etc. In this dictionary such English forms, being always adjacent to their obvious primitives, are usually left without etymological note.
6. n. 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
7. n. in the somatic idioplasm of the hereditary qualities of a group of cells or a part of a developing embryo or growing organism. The term is used therefore with two meanings—to designate the bearer of the hereditary qualities of the ancestral idioplasm, or germ-plasm, which may give rise to a new and complete organism, and to designate the bearer of the hereditary qualities of the idioplasm of successive stages in the development and growth of the organism that arises from the egg. The id of this somatic idioplasm is held to be at first identical with that of the germ-plasm, but to become broken up into simpler and simpler ids as development advances. See idioplasm, doctrine of germ-plasm.
8. n. 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.
9. n. 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.

Wiktionary

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

GNU Webster's 1913

1. n. any document testifying to teh identity of the bearer, especially a card or badge.
2. n. (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.
3. n. (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.

WordNet 3.0

1. n. a card or badge used to identify the bearer
2. n. a state in the Rocky Mountains
3. n. (psychoanalysis) primitive instincts and energies underlying all psychic activity