Apostrophe occurs when a narrator or speaker directly addresses an absent (or deceased) person, an object, an abstract idea, or something imagined as if the addressee were a present and hear and understand them. Apostrophe often begin with the oracular “O.” 

Apostrophe derives from the Greek word apostrephein, meaning “to turn away,” from the words apo (“from”) and strephein (“to turn”).

An example of apostrophe is John Donne’s sonnet “Death, Be Not Proud”:

Death be not proud, though some have called thee 

Mighty and dreadful, for, thou art not so,

For, those, whom thou think’st, thou dost overthrow,

Die not, poor death, nor yet canst thou kill me

In this poem, Donne addresses death directly, as though it were a sentient being capable of understanding what he says. 

Apostrophe can also be found in Mary Shelley’s novel Frankenstein:

Oh! Stars and clouds and winds, ye are all about to mock me; if ye really pity me, crush sensation and memory; let me become as nought; but if not, depart, depart, and leave me in darkness.

In this passage from chapter 17, Victor Frankenstein implores the stars, clouds, and winds to either destroy him or leave him alone.

Other examples:

• “O Captain! my Captain! rise up and hear the bells . . .”
• In Walt Whitman’s poem “O Captain! My Captain!” the speaker directly addresses his dead captain.
• “Oh! Stars and clouds and winds, ye are all about to mock me . . .”
• In Mary Shelley’s Frankenstein, Victor directly addresses the stars, clouds, and winds.
• “Death be not proud, though some have called thee / Mighty and dreadful, for thou art not so . . .”
• In John Donne’s sonnet “Death Be Not Proud,” the speaker directly addresses Death.
• “Is this a dagger which I see before me, / The handle toward my hand? / Come, let me clutch thee! / I have thee not, and yet I see thee still.”
• In Act 2, Scene 1 of Shakespeare’s Macbeth, Macbeth directly addresses an imagined dagger.