Nother is a real word, though most people only notice it inside another or in the expression a whole nother. It is not simply a mistake invented by modern speakers.
Historically, English sometimes split words in ways that feel unusual today. The older phrase an other gradually became another. That means nother has long existed as a meaningful part of the expression, even if it rarely stands alone in standard modern writing.
You can see it in two common places:
- Inside another: Take another piece.
- In the phrase a whole nother: That is a whole nother problem.
Some style guides still treat a whole nother as informal, so it is better suited to conversation or casual writing than to very formal prose. But calling nother unreal would be inaccurate. It has historical roots, and modern English speakers still use it in a recognizable way.
