呉音, (goon in Japanese, two syllables) or if you’re reading this without the correct fonts installed, ⬜⬜, is usually glossed on the web as “Wu dynasty reading”. The background here is that there isn’t just a difference in written Japanese between the native vocabulary and the Sino-Japanese vocabulary, but that Chinese words borrowed at different times and hence with different pronunciations, might be written with the same character.
I knew roughly when the Tang Dynasty were, and the Song. But what about the Wu? They must have been the ones before the Tang.
Except they weren’t. That was the Sui (隋). And going back further, all we find is the state of Wu, which was conquered about a millennium before the first signs of Japanese writing with Chinese characters.
What seems to be the case is that the 呉音 borrowings are named after the state of Wu, and someone somewhere has inadvertently written “Wu dynasty reading” by analogy with 唐宋音, which is usually translated as “Tang dynasty reading”, even though there is yet another set of borrowings elsewhen during the Tang and the second character, 宋, stands for the Song dynasty.
Han readings (漢音) aren’t from the Han dynasty either.