What exactly is happening when we use the same word twice in a row? [duplicate]

Example:

A: Hey, I just bought a mouse.
B: A mouse mouse? Or a computer mouse?

What is this exactly? And are there any rules?

Solution 1:

This is a kind of retronym. It has been called contrastive focus reduplication.

Solution 2:

Rhetorically, there is, by implication, a combination of synecdoche and metonymy involved in the "mouse mouse" locution.

These two figures of speech involve part-to-whole relationships and/or the substitution of parts-to-whole relationships.

All hands on deck [implied is "the deck of the ship"]

is metonymic because the word hands is a substitute for the word sailors. Yes, hands are part and parcel of sailors' bodies, but those hands are also, synecdochally, parts of a whole.

"Mouse mouse," then, means in essence "a real mouse" (or perhaps more accurately, a "live mouse" or a "flesh and blood mouse"). Just as a computer mouse imitates a real mouse by being small, having a "tail" (if it's a wired mouse, that is), and moving around the mouse pad in little and quick movements, so also does the real mouse by virtue of being small, having a tail, and moving about in little and quick movements, correspond synecdochally to the faux (computer) mouse.

This inter-correspondence or analogical similarity of features is at the heart of the way the synecdoche/metonymy figure is employed in the "mouse mouse" locution.