it

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

• pronoun Used to refer to that one previously mentioned. Used of a nonhuman entity; an animate being whose sex is unspecified, unknown, or irrelevant; a group of objects or individuals; an action; or an abstraction.
• pronoun Used as the subject of an impersonal verb.
• pronoun Used as an anticipatory subject or object.
• pronoun Used as an anticipatory subject to emphasize a term that is not itself a subject.
• pronoun Used to refer to a general condition or state of affairs.
• pronoun Used to refer to a crucial situation or culmination.
• pronoun Informal Used to refer to something that is the best, the most desirable, or without equal.
• pronoun Games Used to designate a player, as in tag, who attempts to find or catch the other players.
• noun An animal that has been neutered.
• idiom (with it) Aware of or knowledgeable about the latest trends or developments.
• idiom (with it) Mentally responsive and perceptive.

from The Century Dictionary.

• A personal pronoun, of the third person and neuter gender, corresponding to the masculine he and the feminine she, and having the same plural forms, they, their, them.
• As the nominative of an impersonal verb or verb used impersonally, when the thing for which it stands is expressed or implied by the verb itself: as, it rains (the rain rains or is falling); it is blowing (the wind is blowing).
• As the grammatical subject of a clause of which the logical subject is a phrase or clause, generally following, and regarded as in apposition with it: as, it is said that he has won the prize; he is poor, it is true, but he is honest; it behooves you to bestir yourself; it is they that have done this mischief.
• After an intransitive verb, used transitively for the kind of action denoted or suggested by the verb: as, to foot it all the way to town.
• The possessive case, originally his (see he), now its; the form it without the possessive suffix having been used for a time in works written during the period of transition from the use of his to that of its.
• In children's games, that player who is called upon to perform some particular task, as in I-spy or tag the one who must catch or touch the other players: as, he's it; who's it?
• A dialectal (Scotch) form of -ed, -ed.
• A common abbreviation of Italian.
• noun An abbreviation of Italy.

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

• pronoun The neuter pronoun of the third person, corresponding to the masculine pronoun he and the feminine she, and having the same plural (they, their or theirs, them).
• pronoun See Itself.

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

• abbreviation language Italian.
• abbreviation Italy.
• pronoun The third-person singular personal pronoun used to refer to an inanimate object, to an inanimate thing with no or unknown sex or gender.
• pronoun The third-person singular personal pronoun used to refer to an animate entity of unknown gender.
• pronoun Used to refer to oneself when identifying oneself, often on the phone, but not limited to this situation.
• pronoun The impersonal pronoun, used without referent as the subject of an impersonal verb or statement. (known as the dummy pronoun or weather it)
• pronoun The impersonal pronoun, used as a placeholder for a delayed subject, or less commonly, object. (known as the dummy pronoun or, more formally in linguistics, a syntactic expletive)
• pronoun obsolete, relative That which; what.
• noun One who is neither a he nor a she; a creature; a dehumanized being.
• noun The person who chases and try to catch the other players in the playground game of tag.
• noun UK, uncountable The game of tag.
• adjective colloquial most fashionable.

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

• noun the branch of engineering that deals with the use of computers and telecommunications to retrieve and store and transmit information