my

We don’t traditionally think of my as having synonyms, but there are several situations in which it can replace—or be replaced with—another term.

my own 

The phrase my own is sometimes used as a more emphatic way of saying my, as in I can’t believe I was betrayed by my own family.

mine

Sometimes you can reword what you’re saying to use mine instead of my. For example, instead of saying This is my seat, you could say This seat is mine. 

Mine is also an archaic form of my. This was especially used before a word beginning with a vowel sound, as in mine eyes, or following a noun, as in I must do what is duty mine. 

our

Instead of saying things like This is my house and her house, we use the plural form our, as in This is our house. 

me

Sometimes, my is used where the word me could also be used, such as in sentences like this: Did you hear about my getting promoted? Historically, it was considered more proper to use my before gerunds (e.g., getting in the preceding example), but using me is now more common and often sounds more natural.

Me is sometimes used in place of my in a particularly informal dialectical use in the U.K. and other places, as in I’ll collect me things and be on me way.

Strictly speaking, my doesn’t have a definitive antonym in the same sense that short is the antonym of long. Of course, possession and association are often distinguished by using contrasting possessives, such as in statements like This is my responsibility—it’s not your responsibility. In this sense, all of the other possessive words could be considered the opposite of my, including your, her, his, and their.

On the other hand, one person’s possession of something does not mean that someone else can’t possess it as well. This is indicated in a lot of popular expressions, such as what’s mine is yours, mi casa es su casa, and this land is your land; this land is my land.

My is the possessive form of the singular personal pronoun I. It’s often considered a possessive pronoun, but it functions as a possessive adjective (also called a possessive determiner). That’s a lot of labels for such a common word, but they essentially mean this: my shows possession by functioning as an adjective and modifying a noun (it never functions as a noun itself). The same thing can be said about our. (The forms mine and ours stand alone as nouns and never accompany another noun as modifiers.)

In contrast, the word his can be used as both a possessive pronoun (as in That jacket is his) or a possessive adjective (as in That is his jacket). Possessive words like my commonly indicate possession or ownership, but they can also indicate things other than literal possession, like origin or other qualities (such as in phrases like my country).

My is used along with first person pronouns (like I and me), which refer to the speaker or writer themselves. Other first person possessive forms include mine, our, and ours. In contrast, second person pronouns (like you and yourself) are used to address the person being spoken to or reading. Possessive forms of these include your and yours. Third person pronouns (like he, she, they, him, her, and them) refer to anyone other than the person doing the addressing or the ones being addressed. Third person possessive forms include his, her, hers, their, and theirs.