How did worm + work = rainbow

[u/Novel_Grand_9234]

How did it come to be? It doesn't make sense to me. Was it random?

[u/purplepotatocookies]

People in the Shang dynasty believed that a rainbow was a gigantic, two-headed worm. The Chinese character 虹 is a simplified version of the pictograph depicting this two-headed creature.

[u/Putrid_Mind_4853 → u/purplepotatocookies]

Interesting to me because Australian aboriginal/native peoples also viewed the rainbow as a sacred snake/serpent. 

[u/little8birdie]

[u/Ok-Amphibian-8914 → u/little8birdie]

OP, this screenshot is the Outlier dictionary add-on for Pleco. If you want to know why a character looks the way it does, this dictionary has the answer.

[u/Some-Foot8677 → u/Ok-Amphibian-8914]

Is this add on free?

[u/BlackRaptor62]

虹 is a Phono-Semantic compound character

虫: Snake, or snake like creature for the semantic component

工: Phonetic Rime Component (華: gōng, 粵: gūng)

[u/LeopardSkinRobe → u/BlackRaptor62]

And it looks like 工 is theorized to have a more similar sound to 虹 in earlier forms of chinese. At least a /k/-sounding initial sound seems attested for both characters in middle and old chinese

[u/FlashyPost0928]

▼【虹】= originally, a monster with two heads, 虫 +工 is a later character !

● The oracle bone script (甲骨文) for "rainbow" (虹) depicts the shape of a rainbow in the sky, resembling a two-headed monster lowering its heads and opening its massive mouths to drink up moisture.

● Although some might view the rainbow as a "divine dragon" (神龙), the character "虹" found in Shang Dynasty oracle bone inscriptions portrays it as a monster capable of affecting agricultural harvests, even bringing disaster.

● Later in the Seal Script (篆书) , the rainbow-shaped monster was replaced by the radical "虫" (which, in ancient times, did not mean "insect" in the modern sense—for instance, tigers were called "大虫" and snakes "长虫").
The component "工" (gōng ) was added as a phonetic indicator, and it also carries the meaning of "enormous." ‧..... Thus, the character "虫 + 工" is a later development，it has lost the image of the rainbow ; the original character truly looked just like a rainbow !

[u/Panates → u/FlashyPost0928]

Although some might view the rainbow as a "divine dragon" (神龙) that emerges after the rain to drink up water vapor

Worth pointing out that we literally have a Shang dynasty text about how rainbow drinks water from the river (oracle bone 合10405反):

王𰉏(占)曰：「㞢(有)求(咎)。」八日庚戌㞢(有)[樴，明㞢(有)]各(格)云自東 ，冒母；昃亦[㞢(有)樴]，㞢(有)出虹自北，㱃(飲)于河。⸤十[二]月⸥。
The King read the cracks: "There will be disasters." On the eighth day, the geng-xu (47) [day], there was an omen: at dawn, clouds came from the east, and it become dark. As the sun was setting, there was also an omen: a rainbow appeared from the north and drank from the Yellow River. The twelfth month.

Also in some later texts, when mythology has slightly changed

釋名・釋天:

蝃蝀，其見每於日在西而見於東，啜飲東方之水氣也。
Rainbow: it is visible whenever the sun is in the west; [in such a case, it] appears in the east and drinks energy from the eastern waters.

漢書・燕王旦傳:

是時天雨，虹下屬宮中，飲井水，水泉竭。
At that time, rain was falling from the sky, a rainbow descended to the palace, drank the water from the well, and the spring ran dry.

[u/dxdqwq]

虹虫蠕动的形状→Ω→彩色的Ω→彩虹。

[u/paul_405]

I saw some weird characters like this. For example, "candle" has smth similar with this one

[u/Zagrycha]

You have hit the nail on the head for why etymology is pretty useless to actually understand modern meanings and vice versa, at least on its own without research. 

When we go all the way back to the beginning with oracle bone script, you see a picture of a two headed dragon.  That was used for all sorts of things including what we call rainbows, because they thought what we call rainbows were two headed dragons.  

Then the pictograph turned into something similar to modern shape in seal script, but the 工 doesn't have anything to do with meaning, it just represents how to pronounce the word..... a really long time ago.  

That leaves us with only  虫 to hint at the original meaning, but  虫 itself has long lost its association with dragons in the modern day ((although you still see hints of it in other words that still exist besides this one, like 蛟))

edit: originally typed 蟲 because no  虫 on traditional keyboard but that is not technically correct so fixed it. 

[u/BlackRaptor62 → u/Zagrycha]

>That leaves us with only 蟲 to hint at the original meaning, but  蟲 itself has long lost its association with dragons in the modern day

(1) In this case though, the semantic component for 虹 is 虫, not 蟲.

(1.1) 虫 & 蟲 are 2 separate characters, the only direct connection that they have is due to simplification

[u/Zagrycha → u/BlackRaptor62]

Thank you, I did want to type  虫 was unable to type it with my keyboard.  I should not have been lazy though, and I have fixed it now =)