it's /its/ a contraction of it is or it has

its /its/ possessive or genitive of it¹. (The old form was his, its not being older than the end of the 16c. Its does not occur in the English Bible of 1611 (in Leviticus 25.5 the possessive it was amended to its for the 1660 edition) or in Spenser, rarely in Shakespeare, and is not common until the time of Dryden.)

itself /it-selfˈ/ pronoun

The emphatic and reflexive form of it

by itself

Alone, apart

in itself

By its own nature

it¹ /it/

1. The neuter of he or she and him or her¹applied to a thing without life, a lower animal, a young child, rarely (except as an antecedent or in contempt) to a man or woman
2. Used as an impersonal, indefinite, or anticipatory or provisional subject or object, as the object of a transitive verb that is normally an intransitive, or a noun
3. (in children's games) the player chosen to oppose all others
4. The ne plus ultra, that which answers exactly to what one is looking for (informal)
5. An indefinable crowning quality, personal magnetism
6. Sex appeal, sexual intercourse or activity (informal)

It Girl noun (informal)

A young woman who is, or who makes it her business to be, noted in fashionable circles for her charisma, beauty and wealth

it² /it/ (informal)

Italian vermouth

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