What does 신낭 (腎囊) literally mean?

 ANSWER: a kidney (腎) bag (囊)

My Korean-English dictionary defines the Sino-Korean word 신낭 (腎囊) as "scrotum," but it literally means "kidney (腎) bag (囊)." The 낭 (囊) in 신낭 (腎囊) is the same 낭 used in 배낭 (背囊), which literally means  "back (背) bag (囊)," but which my dictionary defines as "a knapsack" or "a pack."

So, why would Koreans refer to a scrotum" as a "kidney bag"? Probably because a testicle looks similar to a kidney, which looks similar in shape to a "bean." In fact, the pure-Korean word for kidney is 콩팥, which is a word composed of the pure-Korean words "bean (콩)" and "red-bean (팥)." The Sino-Korean word for kidney is 신장 (腎腸).

By the way, a Sino-Korean word for "penis" is 신경 (腎莖), which literally means "kidney (腎) stalk (莖)," which is right next to the "kidney bag (腎囊)."

From Dong-A's Prime Korean-English Dictionary