🔼The name Galatia in the Bible
Galatia was a region in north-central Anatolia (modern Turkey), just south of coastal Paphlagonia, north of Phrygia (to its south-west) and Cappadocia (to its south-east). Galatia became peopled by European Celts who had moved east during the confusing decades that followed the death of Alexander the Great in 323 BC — the famous statue of the Dying Gaul depicts a scene from a battle waged not in France but in Galatia. Its capital was Ancyra, modern Ankara.
By the time of Paul, Galatia bordered the Roman province of Asia Minor (also called Asiana or simply Asia) to its west, but for some reason the Holy Spirit and later Jesus Himself forbade Paul and Timothy to preach in Asia Minor (Acts 16:6-7) and so they hung to its east in Lycaonia (where Derbe and Lystra were) and Galatia and Phrygia. From there they headed for Troas on the western coast and crossed over to Macedonia (modern Greece). On his way back east, Paul passed through Galatia and Phrygia again (18:23)
By the time Paul wrote First Corinthians, the Galatian area was home to multiple churches, which maintained their own monetary economy (1 Corinthians 16:1, also see Galatians 1:2). Somehow these churches became "bewitched" (Galatians 3:1) and succumbed to a "different gospel" (1:6-7), which may have had its roots in Pharisaic Judaism (1:13-14, 2:16, 3:24, 4:5, 5:3) or may even have been of Stoic origin or influence (see 5:22-26). Peter addressed his First Letter to the Galatians and adjacent regions and seems to have had similar concerns (1 Peter 1:1).
While incarcerated in Rome, Paul complained to Timothy that several of his friends had left him, among them Crescens, who had gone off to Galatia (2 Timothy 4:10).
The noun Γαλατης (Galates), meaning Galatian, occurs once (in plural) in Galatians 3:1. The adjective Γαλατικος (Galatikos), meaning Galatian, occurs twice, namely in Acts 16:6 and 18:23, both times in combination with χορα (chora), meaning land or territory.
🔼Etymology of the name Galatia
The name Galatia has nothing to do with the name Gaul, which is related to wah-names such as Wales and Wallonia, but is related to kel-names such as Celts (Κελτοι, Keltoi in Greek). The "Land of the Celts" was known both as "Celtica" (that's Greek) and "Galatia" (that's the Latin transliteration), and both these names were probably derived from the name of some obscure native European tribe, and became applied to whoever lived north of the Alps. In that sense the name Celt (and thus Galatia) means "un-Greco-Roman" and is equivalent to "Barbarian".
By the time of Christ, nobody remembered anymore where the names Celt and Galatia had come from, and their meaning was determined by folk-etymologies and phonetic similarities. Dionysius of Halicarnassus (approximately 60 BC - 7 AD) proposed a few wild myths, among which the tale of some Greek sailors who came to northern Europe and were forced to battle violent winds, and who, upon finally landing their ships named the place after the verb κελλειν (kellein), meaning to put to shore (Roman Antiquities XIV.1). That verb, in turn, is related to the verb κελευω (keleuo), meaning to urge or drive on (in the New Testament this verb is used in the sense of to command; Matthew 8:18, Luke 18:40, Acts 4:15).
Another verbal cluster of interest is that around the adjective κελαινος (kelainos), which means black or dark, and although this word is mostly applied to items upon which the sun doesn't shine (the murky netherworld, for instance), it's also used to describe Ethiopians. Liddell and Scott (A Greek-English Lexicon) suggest that this word may be cognate with κηλις (kelis), meaning stain or blemish, particularly one made by blood (known as the "dark stuff").
But Celtica may surely have been popularly known as the place where the sun doesn't shine (northern Europe from a Mediterranean perspective), which would also have explained why the Celts were so remarkably white. In his History of Rome, Livy reported that the Gauls were more terrifying to look at than other tribes: they were huge and commonly naked from the navel up (22.46), their bodies were strikingly white and they had a habit of fighting naked, to enhanced visual effect (38.21). Diodorus Siculus reported that the Gauls were "white of skin" and endowed with blond hair, which was either naturally blond or bleached with "lime-water" (Library.V.28).
The appearance of milky white fighters in Anatolia probably caused quite a shock, and the formation of the name Galatia was quite possibly helped along by the Latin word lac, meaning milk, and its Greek counterpart γαλα (gala):
But on the other hand, the Latin name Gallus (a Gaul or something Gallic) is identical to the noun gallus, which denotes a rooster (whereas gallina means hen). These words came from Sanskrit and are related to the Greek verb γηρυς (gerus), meaning voice, and even the English verbs "to cry" and "to call".
The rooster is obviously proverbially known as a crier and caller, but he's also known for his perceived pride and aggression, which may also have helped the formation of the name Galatia along. Still, the word gallina may have stuck to the bird also because in the Roman empire, chickens were consulted as oracles (their movements about the yard were thought to conveniently say something about the future). Chickens were also routinely fattened by feeding them milk, but the Roman author Columella decreed that farms should avoid having white chickens, since they are easily spotted by predators.
The ancients entertained the concept of "unobtainium"; a fictional or extremely rare substance, perfectly qualified to perform a certain desired function. The Greeks called this extremely rare and greatly desired thing ορνιθων γαλα (orninthon gala) or "bird's milk" and the Romans called it lac gallinaceum or "chicken's milk". But just like our modern word "unobtainium" is deliberately made to look like it describes an element of the periodic table, so do the Roman and Greek terms describe more than just something silly and tap deeply into symbolic jargon.
What the name Galatia formally means is unknown and has been unknown for millennia. But to the Greeks it sounded like Milky-land and to the Romans it sounded like Rooster-land. In both cases the name Galatia represented worlds of meaning, among which Land Of The Criers or Infantonia.