A name for the eastern Black Sea
In English, Colchis names an ancient kingdom and coastal region at the far eastern end of the Black Sea, overlapping what is now western Georgia and adjoining stretches of the Caucasus. Historians use it for a real polity of the first millennium BCE. Readers of classical myth know it as the land of King Aeëtes, his daughter Medea, and the Golden Fleece that Jason and the Argonauts sailed to seize.
The word is a proper noun, not a common English verb or adjective. Tracking the origin of the word Colchis means following a foreign place-name that English borrowed from the classical languages, not a form inherited from Old English.
How the name entered English
English received the name as a learned borrowing. The immediate classical source is Ancient Greek Kolkhís. Latin took that over as Colchis, a feminine third-declension noun whose genitive Colchidis still shows the Greek stem. School Latin, translations of Ovid and other mythographers, and later geography all kept the Latin spelling, which became the usual English form.
The name was already in English well before modern dictionaries treated it as a headword. In the 1380s Geoffrey Chaucer wrote of Jason reaching Colchos in the Legend of Good Women, using a medieval spelling of the sort English and French often gave to Greek and Latin names in -is. By the late sixteenth century the Latinate Colchis was current enough for John Gerard, in his 1597 Herbal, to explain meadow saffron by pointing to an isle he called Colchis. The modern English adjective and noun Colchian is built on the same stem with the ordinary English suffix -ian.
Dutch Colchis, German Kolchis, French Colchide, Italian Colchide, Spanish Cólquide, and Russian Kolkhida are sister borrowings from the same Greek and Latin stock. Georgian has Kolkheti and Kolkha as local adaptations of the classical name, but the older Georgian historical name for the same western lands is Egrisi, from a native Kartvelian root related to Mingrelian. Colchis is therefore an exonym: the name outsiders used for a country that had its own word.
Greek morphology and an older Caucasian form
In Ancient Greek the place-name Kolkhís is formed from Kolkhós, a word for an inhabitant of that land, plus the feminine suffix -ís. The ethnic noun came first; the country name is the land of the Kolkhoi. That is ordinary Greek morphology, not a later folk story about Jason or gold.
The ethnic name itself is not Greek in origin. Behind the Greek form most scholars place Urartian Qulḫa, also cited as Kilkhi or Kulkha, a land named in cuneiform of the kingdom of Urartu. King Sarduri II recorded campaigns against Qulḫa in the mid-eighth century BCE, around 749–746 BCE. That identification with later Greek Colchis is widely accepted, but it is not a simple equation of two identical maps.
The location of Qulḫa is still argued over. Some place it toward the western Georgian Black Sea coast that classical writers later called Colchis. Others argue for a more southerly district, near modern Göle in northeastern Turkey. Even if the Greek name descends from the Urartian one, the Greeks may have attached it to a different stretch of country, and mythic Aia-Colchis is not always the same thing as the historical land of Colchis in Greek usage. Those are live uncertainties. A tidy single homeland for the name cannot be forced from the evidence.
Greek literature itself shows a lag between people and place. Fragments of Eumelus of Corinth, in the eighth century BCE, already speak of the Colchian land. Fifth-century writers such as Aeschylus and Pindar are often credited with using Kolkhís as a geographic name. Earlier Greek tradition could talk of Kolchians, of Aeëtes, and of the city Aea without always naming a country called Colchis.
What the name has meant
The English word has not drifted far from that classical job. It still labels the ancient region and, by extension, the setting of the Argonaut story. It does not have a chain of everyday senses the way a common noun or verb does.
Latin usage was slightly broader. Beside the country, Colchis could name a Colchian woman, often with Medea in view. English mostly kept the toponym and let Colchian do the work of describing people and things from that land.
The name did spawn a botanical and medical family in English. Greek kolkhikon, the neuter of an adjective meaning of Colchis, named a poisonous autumn-flowering plant later called meadow saffron. Latin and then English took it as colchicum, first recorded in English in Gerard in 1597. From that plant English later drew colchicine. Ancient writers associated Colchis with potent drugs because myth made Medea a sorceress; Roman poetry even had a stock phrase for Colchian poisons. The plant name is a semantic offshoot, not a change in the place-name itself.
After the classical kingdom faded, later writers used other names for successor polities on the same coast, notably Lazica. The English word Colchis stayed attached to the ancient and mythical layer.
A name that outlived its kingdom
One durable fact is how little English remade the word. The usual modern spelling is still Latin. The older English Colchos in Chaucer shows the name arriving through medieval story rather than through trade slang. The likely deeper source, Urartian Qulḫa, is older than the Greek poets who made the land famous, even if scholars still argue over where that Urartian land sat on the map.
The takeaway sits in a garden bed. When English borrowed colchicum for meadow saffron, it was still pointing, through Greek, at Colchis: a Caucasian kingdom whose name Greek had already reshaped from an earlier local form, and whose mythic reputation for dangerous plants was enough to christen a flower.