Meaning
What does Imouto mean?
Origin
What's the origin of Imouto?
Spread & Usage
How did Imouto spread?
Thanks to message boards, forums and blogs revolving around anime and manga, the phrase got adopted in plenty of peoples’ dictionaries.
The influence of hentai also helped rooting the term in English, mostly because of the massive amount of incest and lolicon hentai being created.
Urban Dictionary added a definition on imouto in 2009, to enlighten all to-be otakus.

External resources
- Honey’s Anime – What Does Imouto Mean?
- Urban Dictionary – Imouto