Is there a common etymology for the kanji 巳 and 己 and 已?

Question

The three characters 巳 and 己 and 已 are visually very similar, but do they have a common etymology or any overlap in terms of semantic content?

Any information would be appreciated.

As a starting point to answering this question (ignoring any kanji shape analysis, which is paleogaphy), do a simple comparison between their OC reconstructions. If they sound similar but do not appear to overlap in semantic content, then you can be sure that phonetic loans are appearing somewhere here. — dROOOze, May 31, 2019 at 12:17
What is the best way to compare Old Chinese reconstructions? — kandyman, May 31, 2019 at 12:37
Wiktionary has free information on this taken from Zhengzhang and Baxter-Sagart, e.g. en.wiktionary.org/wiki/%E5%B7%B2#Pronunciation and en.wiktionary.org/wiki/%E5%B7%B3#Pronunciation - FYI: these two are related paleographically. — dROOOze, May 31, 2019 at 12:39

Community · Accepted Answer · 2020-06-17 08:18:27Z

「巳」depicts a type of snake. The word that it represents (Baxter-Sagart OC: /*s-[ɢ]əʔ/, sixth earthly branch) is a phonetic loan.

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「已」(/*ɢ(r)əʔ/, already) was originally the same character as「巳」, and is also a phonetic loan. Much later on, the two meanings (sixth earthly branch and already) were differentiated by writing the character「已」without a fully enclosed loop at the top.
「己」is graphically unrelated to the other two, and the original meaning is unclear. The earliest determined usage is for the word /*k(r)əʔ/, sixth heavenly stem. The meaning self is a phonetic loan.

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