the shape

"忌(ki)"

己＋心＝忌

己(ko,ki)
Today，common meaning of this Chinese character is "oneself".

"State that the person is kneeling.
Long ago，there was a tool to wind the yarn in such a shape in china."
　
Originally of this was the hieroglyphics like that.
　
"I correct my mind like winding yarn.
In short，I must have a proper mind."

Origin of 己.
It seems like that.

"kneeling.
Attitude toward older people."
　
And this Chinese character seems to also own this sense originally.
(At first，its object could have been 天.)
　
　
・・・・・・・・・　
　
　
心(shin)
Today，common meaning of this Chinese character is "heart" or "mind".
And this Chinese character was the hieroglyphics heart of organ.

己＋心＝忌

Common meaning of 忌 is "contraindicated" of course.

Well，origin of 諱.
(Common meaning of 諱 is also "contraindicated" of course.)

"Specific word.
I want to go away from it."
　
It seems like that.　
And origin of 忌.

"Superior persons than me.
I must hesitate to them.
So I want to evasion them."

It seems like that.
　

・・・・・・・・・　
　

"The anniversary of the ancestor or parent death."
　
忌 also have this meaning.
But 諱 have not this meaning.
　
Both pronunciations is "ki".
　
Therefore，the shape of the Chinese character of both.
Ancient Chinese people might had been distinguish the fine nuances by it.
　
Or by pronunciation of phrase that contains its Chinese characters.