mine

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

my

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

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. 

my own 

The phrase my own is sometimes used as a more emphatic way of saying mine, as in The fault is my own.

ours

Instead of saying things like This house is mine and hers, we usually use the plural form ours, as in This house is ours.

Strictly speaking, mine 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 responsibility is mine—it’s not yours. In this sense, all of the other possessive words could be considered the opposite of mine, including yours, hers, his, and theirs.

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.

Mine is a pronoun. It’s a form of the possessive case of the personal pronoun I that’s used as a predicate adjective (a type of adjective that modifies or describes the subject of a sentence or clause and is linked to the subject by a linking verb, such as a form of the verb be), as in That pencil is mine. It can also be used as a pronoun that functions as the subject, as in Mine is the red one. 

Like the similar possessive words yours, hers, theirs, and ours, mine stands alone and typically never accompanies another noun as a modifier.

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).

Mine 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 my, 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.