The noun νεφρος (nephros) primarily means kidney, and hence occurs in the classics mostly in the plural: νεφροι (nephroi). This word may look like it has something to do with νεφελη (nephos), cloud, but it really doesn't. Instead, our noun νεφρος (nephros) derives from the widely attested Proto-Indo-European noun "neg-ros", also meaning kidney (hence the German and Dutch noun Nier, kidney).

It's formally unclear where this word "neg-ros" comes from, but intuitively one may think of the root "neg-", naked or bare, from which also stem the Latin word for black, niger (hence also noir), and night, nox, and even the Greek word γυμνος (gumnos), naked (evidently since during the day we humans are dressed, but also since daylight was considered the robe of the deity: see Isaiah 6:1). The second part of our word may have something to do with the PIE adjective "hrowdos", red, from the root "hrewd-", to be red. And since in both Indo-European and Semitic languages alike, the color red is the color of beginnings — see our articles on red-names like Adam, the Red Sea and Rhodes — our proverbially dark-red kidneys embody one's most fundamental self, the seat of one's most primitive sentiments.

And that takes us to our word's secondary meaning in the Greek classics, namely that of testicle. It's probably not correct to speak of a euphemism or metaphor since in Greek classical times, testicles were not so zealously obscured as to merit euphemisms. Instead, our word probably referred to someone's most inner self, and just like the single same act of circumcision befell both a man's external penis and his internal heart (Deuteronomy 10:16), so our word νεφροι (nephroi) both described one's external and internal knödels.

In our article on the verb כבד (kabed), meaning to be or seem heavy or impressive, we observe that the noun כבד (kabed), which is usually thought to denote the liver, or the 'heavy one' or 'weight-gainer' among the organs, occurs in priestly regulations continuously correlated with two organs called כלית (klyt, in plural), which are thought to denote the kidneys. Here at Abarim Publications, however, we suspect that this noun כבד (kabed) also (or more so) describes the penis, and the כלית (klyt) the associated testicles (note the otherwise inexplicable Dutch word for testicle: kloot). The priestly regulations are not specific enough to derive which organs they describe, but while in agony over "the destruction of the daughter of my people", the prophet Jeremiah speaks of the כבד (kabed) pouring out over the earth, which is an obvious reference to spilled seed (Lamentations 2:11, see Genesis 28:9).

In our article on the noun μεμβρανα (membrana), parchment, we show how the first two words of the Bible, namely בראשית ברא (bresheet bera), which means "in the beginning created", also looks like a case of broken symmetry: ברא־שית ברא (bera-syt bera), which obviously corresponds to the waters-heaven-waters broken symmetry of the second creation day, which (still obviously) illustrates the divine scrotum as it relates to the feminine two ovaries: one of which provides the ovum from which the dry land emerges. Similar broken symmetries occur all over the Bible, probably most spectacularly in the image of Christ on Golgotha, as he hangs between two murderers, one of whom is lost forever while the other binds himself to Christ eternally.

Our noun νεφρος (nephros) occurs in the New Testament in Revelation 2:23 only, in the term νεφροι και καρδιαι (nephroi kai kardiai), which means kidneys-and-hearts, and it means testicles-and-penises, and it means ovaries-and-wombs.