What figure of speech involves addressing an absent or imaginary person or thing, like saying "Death where art thou sting?"?

The correct answer is apostrophe, which is a figure of speech used to address an absent or imaginary entity as if it were present and capable of responding. This technique allows the speaker to express thoughts and feelings directly to someone who cannot respond, therefore emphasizing aspects of emotion and depth in communication. In the provided example, "Death where art thou sting?" the speaker is directly addressing Death, an abstract concept, allowing for an exploration of themes surrounding mortality and the human experience.

In contrast, the other options represent different rhetorical devices that do not match this function. Colloquy typically refers to a conversation or dialogue, often between two or more people, rather than addressing an absent figure. Metonymy involves substituting the name of one thing with the name of something closely associated with it, while synecdoche uses a part of something to represent the whole or vice versa. Neither of these conveys the direct address to a non-present entity as apostrophe does.