The Collaborative International Dictionary of English v.0.48:

ID \ID\, ID \I.D.\([imac]`d[=e]"), n. [capitalized] [shortened
   form of identification.]
   any document testifying to the identity of the bearer,
   especially a card or badge.

   Syn: ID.
        [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

I'd \I'd\
   A contraction from I would or I had; as, I'd go if I could.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Id \Id\, n. (Zool.)
   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.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

id \id\ ([i^]d), 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.
   [PJC]

The Collaborative International Dictionary of English v.0.48:

Idem \I"dem\, pron. or adj. [L.]
   The same; the same as above; -- often abbreviated id.
   [1913 Webster]