Or 何故
一文字 comes up from time to time on our forums here. I think someone else mentioned it earlier this year.
Found it: My wife seems to be skeptical of the usefulness regarding some of the vocab on Wanikani
We already had the 河豚 incident and before that the 里心 incident, which I did not witness personally.
WaniKani prioritizes kanji readings over vocab and overall usefulness, something we have to get used to . However, to kind of reiterate the take-home from the 河豚 incident, it’s worth knowing a word, because there is a chance we’ll come across it eventually.