it

American Heritage® Dictionary of the English Language, Fourth Edition

1. pro. 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: polished the table until it shone; couldn't find out who it was; opened the meeting by calling it to order.
2. pro. Used as the subject of an impersonal verb: It is snowing.
3. pro. Used as an anticipatory subject or object: Is it certain that they will win?
4. pro. Used as an anticipatory subject to emphasize a term that is not itself a subject: It was on Friday that all the snow fell.
5. pro. Used to refer to a general condition or state of affairs: She couldn't stand it.
6. pro. Used to refer to a crucial situation or culmination: This is it—the rivals are finally face to face. That's it! I won't tolerate any more foolishness.
7. pro. Informal Used to refer to something that is the best, the most desirable, or without equal: He thinks he's it. That steak was really it!
8. n. Games A player, as in tag, who attempts to find or catch the other players.
9. n. An animal that has been neutered: The cat is an it.
10. idiom. with it Slang Aware of or knowledgeable about the latest trends or developments.
11. idiom. with it Slang Mentally responsive and perceptive: I'm just not with it today.

Century Dictionary and Cyclopedia

1. 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. A substitute for the name of an object (previously mentioned, or understood from the context or circumstances) not regarded as possessing sex, or without regard to the sex, or for an abstract noun, a phrase, or a clause: as, it (a stone) is very heavy; feed it (an infant) with a spoon; the moon was red when it rose; the horse stumbles when it (or he) is driven fast; how did it (an event) happen? It is often used vaguely for a thing, notion, or circumstance not definitely conceived, or left to the imagination: as, how far do you call it? plague take it! you'll catch it!
2. 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).
3. 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.
4. 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.
5. 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.
6. 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? [In old usage the substantive verb after it often agrees with the succeeding nominative in the first or second person: as, “It am I, fader,” in Chaucer.]
7. A common abbreviation of Italian.
8. A dialectal (Scotch) form of -ed, -ed.
9. n. An abbreviation of Italy.

Wiktionary

1. abbr. language Italian.
2. abbr. Italy.
3. pro. The third-person singular personal pronoun used to refer to an inanimate object, to an inanimate thing with no or unknown sex or gender.
4. pro. The third-person singular personal pronoun used to refer to an animate entity of unknown gender.
5. pro. Used to refer to oneself when identifying oneself, often on the phone, but not limited to this situation.
6. pro. The impersonal pronoun, used without referent as the subject of an impersonal verb or statement. (known as the dummy pronoun or weather it)
7. pro. 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)
8. pro. obsolete, relative That which; what.
9. n. One who is neither a he nor a she; a creature; a dehumanized being.
10. n. The person who chases and try to catch the other players in the playground game of tag.
11. n. UK, uncountable The game of tag.
12. adj. colloquial most fashionable.

GNU Webster's 1913

1. pro. 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).

WordNet 3.0

1. n. the branch of engineering that deals with the use of computers and telecommunications to retrieve and store and transmit information