Why is ふい written in hiragana?


I reckon that ふい is a kango word (不意), but I usually see it written in
hiragana, even in print. Neither of the two characters are hard, and if people
are typing it shouldn't matter that ふい is easier to write, so I wonder if
there are any other reason why ふい is usually writtein in hiragana.




There are two different ふい listed in dictionaries:

  * **不意** ([jisho.org](http://jisho.org/word/%E4%B8%8D%E6%84%8F), [デジタル大辞泉](https://dictionary.goo.ne.jp/jn/189807/meaning/m0u/)): sudden; abrupt; unexpected; unforeseen​
  * **ふい** ([jisho.org](http://jisho.org/word/%E3%81%B5%E3%81%84), [デジタル大辞泉](https://dictionary.goo.ne.jp/jn/189803/meaning/m0u/%E3%81%B5%E3%81%84/)): coming to nothing; ending without result; total waste​

The second one has nothing to do with 不意, and has to be written in hiragana.
That is, you can say 不意に思い出す but not チャンスを不意にする nor チャンスが不意になる.

According to
[this](https://detail.chiebukuro.yahoo.co.jp/qa/question_detail/q13166494763),
ふい meaning _total waste_ may be etymologically related to 吹く.

In addition, ふいに meaning _unexpectedly_ is often written in kana these days,
and I think that's because this ふいに is becoming a lexicalized adverb, which
should be [generally written in kana](http://www.yamanouchi-
yri.com/yrihp/techwrt-2-4s/t-2-4s03a.htm). (We still can say 不意の～, but I have
never heard ～は不意だ.) 次第に and 遂に are other examples of adverbs which are
commonly written in hiragana.




There are two different ふい listed in dictionaries:

  * **不意** ([jisho.org](http://jisho.org/word/%E4%B8%8D%E6%84%8F), [デジタル大辞泉](https://dictionary.goo.ne.jp/jn/189807/meaning/m0u/)): sudden; abrupt; unexpected; unforeseen​
  * **ふい** ([jisho.org](http://jisho.org/word/%E3%81%B5%E3%81%84), [デジタル大辞泉](https://dictionary.goo.ne.jp/jn/189803/meaning/m0u/%E3%81%B5%E3%81%84/)): coming to nothing; ending without result; total waste​

The second one has nothing to do with 不意, and has to be written in hiragana.
That is, you can say 不意に思い出す but not チャンスを不意にする nor チャンスが不意になる.

According to
[this](https://detail.chiebukuro.yahoo.co.jp/qa/question_detail/q13166494763),
ふい meaning _total waste_ may be etymologically related to 吹く.

In addition, ふいに meaning _unexpectedly_ is often written in kana these days,
and I think that's because this ふいに is becoming a lexicalized adverb, which
should be [generally written in kana](http://www.yamanouchi-
yri.com/yrihp/techwrt-2-4s/t-2-4s03a.htm). (We still can say 不意の～, but I have
never heard ～は不意だ.) 次第に and 遂に are other examples of adverbs which are
commonly written in hiragana.

