The verb ζωννυμι (zonnumi) or ζωννυω (zonnuo) means to gird, to bind articles of clothing together at the waist, or οσφυς (osphus), loin (see below). Our word is thought to derive from a Proto-Indo-European root "yehs-", to gird.

Pretty much all outfits in antiquity involved belts and girdles, and our verb could describe any kind of bundling or binding by means of belts. Specifically it was used to describe soldiers who would strap on their swords for war. As such our verb would have a connotation of getting ready for whatever action, which is how Paul spoke of loins girded with the truth (Ephesians 6:14, see Isaiah 11:5 and 59:17).

Also rather specifically, our verb was used in antiquity to describe how athletes would gird themselves with loin cloths. However, at some point in the 15th Olympic Games of 720 BC, a runner named Orsippus had somehow managed to get separated from his loincloth, and merrily flopped on in the buff. Orsippus won his race, and became subsequently known as the first to be crowned naked: the victor over all the girdled losers. The sight of Orsippus wearing nothing but a crown was evidently so inspiring that the Greeks swore to never again be pressed to compete girdled. This is why the Greeks sported naked (our word "gym" derives from the Greek adjective γυμνος, gumnos, meaning naked) and since the Greek ways were considered the best, the wearing of a sport girdle was considered a barbarism that only unsophisticated buffoons engaged in. All this also sheds some extra light on Paul's few sport metaphors (1 Corinthians 9:23-27; see Revelation 3:18, Exodus 20:26, Leviticus 18:6).

In the New Testament, our verb is used twice in John 21:18 only, as synonym of to dress, or rather more elaborate: to bind one's outfit together. From our verb derive:

The noun οσφυς (osphus) means "loin" and, judging from its contexts in the classics, denotes the area of the lower back and belly, including the reproductive organs (Hebrews 7:10). Since the lower belly was the seat of one's basest emotions, and the genitalia the seat of one's will — see our lengthy article on ירך (yarek), male and female genitalia — the loins were to be guarded for a wide range of reasons.

Jesus said: "keep your loins girded and your lamps lit" (Luke 12:35), which not only means "keep your pants on and your eyes open" but also "keep your lower emotions in check and your rational mind informed." The Hebrew word for loins, namely כסל (kesel), also means stupidity or confidence (of the misplaced kind, or so it's implied). The loftier counterpart of the οσφυς (osphus) was the θωραξ (thorax), upper body.

Paul spoke of loins girded with the truth, which also refers to the sword or utility knife that people like fishermen, butchers and soldiers commonly carried on their hip: see our article on the noun μαχαιρα (machaira), knife or sword. Peter spoke of the "loins of the mind" (1 Peter 1:13), which is not a great leap from "circumcision of the heart" (Deuteronomy 10:16, Romans 2:29; and see our lengthy article on the verb περιτεμνω, peritemno, to circumcise).

When one wore a long tunic and had to work or run (1 Kings 18:46), one would hoist it up and gird it to one's waist to free one's feet: see our article on רגל (regel), foot, also for a quick look at the often proposed euphemism of feet for genitalia.

Adjective זרזיר (zarzir), means girded and describes some animal (a rooster, perhaps: Proverbs 30:31). This adjective comes from the verb זור (zur III), to press down and out, which is an activity to which the loins are happily equipped. Identical verb זור (zur II) means to be loathsome. Identical verb זור (zur I) means to be foreign.

It's unclear where our noun οσφυς (osphus) comes from, but since the Greek alphabet is an adaptation of the Hebrew one, our word may very well have been imported along with it. A strikingly similar Hebrew verb is אסף ('asap), to gather or collect, mostly in reference to harvests, and with a connotation of removal. Noun אסף ('osep) means gathering. Similar verb סוף (sup) means to come to an end and noun סוף (sop) means end (these words are part of a cluster of words that emphasize division or splitting).

Our noun οσφυς (osphus), loin, is used 8 times in the New Testament; see full concordance. It has no derivatives.