by applying

己.

Pronunciation of this Chinese character.
It is "ki".

"Character of one is the symbolizes of the meaning of new character.
And another character show the sound of new character."
　
Therefore，己 show the sound of 忌(ki) by this law.
And 心(sin) is the symbolizes of the meaning of 忌.
This become like that.

However，己 have a sense of modesty as already mentioned above.
　
"I correct the heart."

This has affected the meaning of 忌.
Therefore，己 is not a Chinese character that only show the sound of 忌.
　
Though，because there is no reason to combine the unnecessary things to each other.
This may be natural.
(Such combinations also might be present of course.)
　
　
・・・・・・・・・
　

Similarly,  韋(i).
This Chinese character also show the sound of 諱(ki).
And the role of this Chinese character also is not only it.

"People go away(舛・↑↓) from the center point(口)."
This also has affected the meaning of 諱.
　
Yes，I wrote strange thing.　

"韋(i) show the sound of 諱(ki)."
　
Pronunciation of 韋 is "i".
So pronunciation of 諱.
It must be "i".
But pronunciation of 諱 is "ki".

Note:Pronunciation of this "i".
Its sound is similar to "i" of India.
　

・・・・・・・・・　
　
　
忌.
　
I examined this character in the glossary of Chinese character.
It called "kango-rin". (漢語林)
　
The sound of the character is "ki".
When reading the character by the Japanese language.
It is "i-mu，i‐mawashī". (忌む，忌まわしい)　

It had been so described..
　
By the way，This "When reading the character by the Japanese language."
This method is called "kun-doku". (訓読)

When examined in the national language dictionary about "kun-doku".

Reading Chinese characters by applying the Japanese language.
Reading Chinese literature according to the grammar of Japanese language.
　
It had been so described.