Kanji that don't use their specified readings


Hello I'm trying to understand something about kanji readings. As far as I
understand each Kanji character has multiple readings and each of these
readings can be used alone or in conjunction with different kanji.

My question is, how is it that sometimes I see words that do not use any
specified reading of the kanji, for example:

日 can be read as ひ, -び, -か，ニチ, ジツ

but in the word いっぴ (一日) it is used as ぴ




First of all, be aware that 一日 is usually read _ichinichi_ , to count one day,
or _tsuitachi_ , when it refers to the first day of a month (as in "April the
1st"). But the phenomenon you spotted in _ippi_ also happens to other words,
so let's talk about that.

The simple explanation of _ippi_ is that, when you join a ち (like いち) to ひ,
the sequence ち-ひ usually becomes っぴ. So you see, the 日 is using its common ひ
reading, after all. It's just that ぴ is considered to be a transformation of ひ
(in this case, triggered by ち). More details follow.

The change from ひ to ぴ is an example of a _sound change_ or _euphony_
(Japanese: 音便{おんびん}). There are two important types of sound change which may
happen when linking words into a compound:

**Sequential voicing** (連濁{れんだく}): The first kana character of the _second_
word may get a _dakuten_ ゛ mark. For example, 棚 たな → 本棚 ほん **だ** な. (In
linguistics terms, the second word becomes
[voiced](https://en.wikipedia.org/wiki/Voice_\(phonetics\)), except if it
begins with an /h/, which becomes /b/. That's because /h/ was /p/ in Old
Japanese, and a voiced /p/ is a /b/.)

If the _kana_ cannot normally be written with a _dakuten_ ゛, then no sound
change happens. Even if it can, sometimes it doesn't change. It's a bit hard
to predict when will _rendaku_ occur ([see
here](https://en.wikipedia.org/wiki/Rendaku)). Just be aware that it does
happen, and with time you'll get a feel for it.

**Gemination** (促音便{そくおんびん}): When two words are linked, the first consonant
of the _second_ word may become doubled ( _gemini_ is Latin for "twins"). The
doubled or "long" consonants are easier to see in rōmaji:

  * 発 _hatsu_ + 達 _tatsu_ → _ha **tt** atsu_
  * 一 _ichi_ + 個 _ko_ → _i **kk** o_
  * 真 _ma_ + 白 _shiro_ = _ma **ss** hiro_

Gemination is often triggered by the first word ending with a つ or ち. In this
case, the trailing つ or ち will become a "small _tsu_ " (that is, the syllable
will disappear, being subsumed into the new geminated consonant):

  * 発 はつ + 達 たつ → 発達 は **っ** たつ
  * 一 いち + 個 こ → 一個 い **っ** こ

A sequence of /k/ sounds also gets geminated, with one /k/-kana becoming a
small _tsu_ :

  * 悪 あく + 化 か → 悪化 あっか 

Sometimes no character becomes a small _tsu_ ; the small _tsu_ seemingly pops
out of nowhere:

  * 真 ま + 白 しろ → 真っ白 まっしろ

Finally, /h/-sounds (は,ひ,ふ,へ,ほ) are special. Whenever a /h/-sound gets
geminated, it becomes a /pp/ sound; that is, the はひふへほ kana get a _handakuten_
゜ mark, becoming ぱぴぷぺぽ. (Again, this is because /h/ used to be /p/ in Old
Japanese). This is what happened to 一日 as いっぴ, and it happens often for
counters starting with 一 いち:

  * 一発 いっぱつ
  * 一匹 いっぴき
  * 一夫 いっぷ
  * 一片 いっぺん
  * 一本 いっぽん




First of all, be aware that 一日 is usually read _ichinichi_ , to count one day,
or _tsuitachi_ , when it refers to the first day of a month (as in "April the
1st"). But the phenomenon you spotted in _ippi_ also happens to other words,
so let's talk about that.

The simple explanation of _ippi_ is that, when you join a ち (like いち) to ひ,
the sequence ち-ひ usually becomes っぴ. So you see, the 日 is using its common ひ
reading, after all. It's just that ぴ is considered to be a transformation of ひ
(in this case, triggered by ち). More details follow.

The change from ひ to ぴ is an example of a _sound change_ or _euphony_
(Japanese: 音便{おんびん}). There are two important types of sound change which may
happen when linking words into a compound:

**Sequential voicing** (連濁{れんだく}): The first kana character of the _second_
word may get a _dakuten_ ゛ mark. For example, 棚 たな → 本棚 ほん **だ** な. (In
linguistics terms, the second word becomes
[voiced](https://en.wikipedia.org/wiki/Voice_\(phonetics\)), except if it
begins with an /h/, which becomes /b/. That's because /h/ was /p/ in Old
Japanese, and a voiced /p/ is a /b/.)

If the _kana_ cannot normally be written with a _dakuten_ ゛, then no sound
change happens. Even if it can, sometimes it doesn't change. It's a bit hard
to predict when will _rendaku_ occur ([see
here](https://en.wikipedia.org/wiki/Rendaku)). Just be aware that it does
happen, and with time you'll get a feel for it.

**Gemination** (促音便{そくおんびん}): When two words are linked, the first consonant
of the _second_ word may become doubled ( _gemini_ is Latin for "twins"). The
doubled or "long" consonants are easier to see in rōmaji:

  * 発 _hatsu_ + 達 _tatsu_ → _ha **tt** atsu_
  * 一 _ichi_ + 個 _ko_ → _i **kk** o_
  * 真 _ma_ + 白 _shiro_ = _ma **ss** hiro_

Gemination is often triggered by the first word ending with a つ or ち. In this
case, the trailing つ or ち will become a "small _tsu_ " (that is, the syllable
will disappear, being subsumed into the new geminated consonant):

  * 発 はつ + 達 たつ → 発達 は **っ** たつ
  * 一 いち + 個 こ → 一個 い **っ** こ

A sequence of /k/ sounds also gets geminated, with one /k/-kana becoming a
small _tsu_ :

  * 悪 あく + 化 か → 悪化 あっか 

Sometimes no character becomes a small _tsu_ ; the small _tsu_ seemingly pops
out of nowhere:

  * 真 ま + 白 しろ → 真っ白 まっしろ

Finally, /h/-sounds (は,ひ,ふ,へ,ほ) are special. Whenever a /h/-sound gets
geminated, it becomes a /pp/ sound; that is, the はひふへほ kana get a _handakuten_
゜ mark, becoming ぱぴぷぺぽ. (Again, this is because /h/ used to be /p/ in Old
Japanese). This is what happened to 一日 as いっぴ, and it happens often for
counters starting with 一 いち:

  * 一発 いっぱつ
  * 一匹 いっぴき
  * 一夫 いっぷ
  * 一片 いっぺん
  * 一本 いっぽん

