Boyd’s Bible Dictionary:

(gird). Worn by men and women to hold the looser garments. Made of leather (2 Kings 1:8; Matt. 3:4); of linen (Jer. 13:1; Ezek. 16:10); embroidered (Dan. 10:5; Rev. 1:13); used for carrying swords and daggers (Judg. 3:16; 2 Sam. 20:8).

Concise Bible Dictionary:

An article of dress always worn in the East, both by the rich and the poor, and needed there because of their flowing robes. For the poor they were of the plainest material, but for the rich they were more or less costly, and were highly ornamented. They were thus suitable articles for presents (1 Sam. 18:4; 2 Sam. 18:11). John the Baptist wore a leathern girdle, or one of skin (Matt. 3:4; Mark 1:6; compare 2 Kings 1:8). In the Revelation the Lord has on a golden girdle, and the seven angels who come out of the temple have the same (Rev. 1:13; Rev. 15:6). The priests wore girdles, and one for Aaron was a “linen” girdle (Lev. 16:4), and with the breastplate was the CURIOUS (that is, embroidered) GIRDLE of the ephod, made of gold, blue, purple, scarlet, and fine-twined linen (Ex. 28:8).
The girdle is typical of strength, and “girding up the loins” denotes active service. When the Gentiles are gathered by God to discipline Israel, the girdle of their loins shall not be loosed (Isa. 5:27). Of the Lord when He comes to reign it is said, “Righteousness shall be the girdle of his loins, and faithfulness the girdle of his reins” (Isa. 11:5). In the present warfare the Christian is exhorted to have his loins “girt about” with truth (Eph. 6:14)—the “truth” being the very thing that Satan will most oppose, and about which the mass are liable to be indifferent.
Girdles were also used for purses (Matt. 10:9; Mark 6:8), where the word signifies a “belt.”

“314. Girdle Running Footmen” From Manners and Customs of the Bible:

1 Kings 18:46. He girded up his loins, and ran before Ahab to the entrance of Jezreel.
1. The girdle is one of the most useful articles of Eastern costume, and frequently the most ornamental of them all. With the long loose dress of the Orientals it becomes a necessity, since it would be difficult to walk or run unless the dress were tightened. Hence Elijah “girded up his loins” as a preparation for running. See also 2 Kings 4:29; 9:1. Thus the Israelites prepared for their exodus (Ex. 12:11). It is also thought to give strength to the body while engaged in severe bodily labor or exercise, and hence the word is sometimes used figuratively to denote strength. See Job 40:7; Psalm 65:6; 93:1.
Girdles are of various sizes, and are made of different materials, from calico to cashmere. The rich use silk or linen, and sometimes decorate their girdles with gold, silver, and precious stones. The poor have them of coarser materials, leather being very commonly used. Elijah’s girdle was of leather (2 Kings 1:8), so also was that of John the Baptist (Matt. 3:4).
Graham thus describes the mode of putting on the girdle. “The girdle is put on thus: your slave having folded it the right breadth, holds it at one end, while you take the other and lay it upon your side, and roll yourself round and round, as tight as possible, till you. arrive at the slave, who remains immovable. If you have no slaves, a hook or the branch of a tree will answer the same purpose” (The Jordan and the Rhine, p. 163). When running, the ends of the outer garment are tucked into the girdle.
2. It is still customary to do honor to a king by running before his chariot; and the same honor is conferred upon persons of less distinction. When Mohammed All came to Jaffa, some years ago, with a large army, to quell the rebellion in Palestine, he had his quarters inside the city, while the camp was on the sand-hills to the south. The officers in their passage from camp to headquarters “were preceded by runners, who always kept just ahead of the horses, no matter how furiously they were ridden; and in order to run with the greater ease, they not only girded their loins very tightly, but also tucked up their loose garments under the girdle, lest they should be incommoded by them” (Thomson, The Land and the Book, vol. 2, p. 227).
Allusion is also made to this custom in 1 Samuel 8:11; 2 Samuel 15:1; 1 Kings 1:5. (See the engraving on the opposite page.)

“318. Military Girdles” From Manners and Customs of the Bible:

1 Kings 20:11. Let not him that girdeth on his harness boast himself as he that putteth it off.
The girdle is used as a convenient place for carrying different weapons. The sword, the dagger, and in modern times the pistol, are placed there. It was thus that Ehud carried his dagger (Judg. 3:16). We are told in 1 Samuel 25:13, that David and his men girded on their swords. Similar allusions to this use of the girdle are made in Deuteronomy 1:41; Psalm 45:3; Song of Solomon 3:8; Isaiah 8:9. The military girdle was not, however, a mere sword-sash, but a strong belt, designed to sustain the body, and at the same time to cover such portion of the abdomen as might be unprotected by the cuirass. Some girdles, indeed, seem to have been a constituent part of the cuirass, intended to fasten it more firmly. The importance of the girdle as a piece of armor is seen in the fact that thorough preparation for the fight is called “girding on.” Paul says: “Stand therefore, having your loins girt about with truth” (Eph. 6:14).
Military girdles were made of stronger materials than those designed for common purposes. Leather, iron, and bronze were used in their construction, and, where rich ornament was required, silver and gold.