Katie Odhner asks:
I have lately been teaching myself Korean and have become quite interested in Sino-Korean vocabulary. Recently two words in particular caught my attention: samchon 삼촌 ("paternal uncle"), from Chinese s ān cùn 三寸 ("three inches"), and sachon 사촌 ("cousin"), from Chinese sì cùn 四寸 ("four inches"). I wondered how "three inches" and "four inches" could turn into family members. According to one website I found, chon 寸 can refer to "degree (of kinship)", which makes some sense. But when I looked on ctext.org (Chinese Text Project), I couldn't find classical Chinese examples of this usage, so I'm thinking maybe it's a Korean invention.
Have you ever encountered cùn 寸 ("inch") in Classical Chinese to refer to degree of kinship? Do you think it's a Korean invention? And does "third degree of kinship" for uncle and "fourth degree of kinship" for cousin have any roots that you can think of in the Confucian tradition, or is that also a native Korean concept?