The Welsh language, like most of the languages of Europe, and many of those of Asia, has evolved from what linguists term Indo-European. Indo-European was spoken about 6000 years ago (4000 BC) by a seminomadic people who lived in the steppe region of Southern Russia. Speakers of the languages migrated eastwards and westwards; they had reached the Danube valley by 3500 BC and India by 2000 BC. The dialects of Indo-European became much differentiated, chiefly because of migration, and evolved into separate languages. So great was the variety among them that it was not until 1786 that the idea was put forward that a Family of Indo-European languages actually exists. In the twentieth century Indo-European languages are spoken in a wide arc from Bengal to Portugal, as well as in countries as distant as New Zealand and Canada, to which they have been carried by more recent emigrants. The Indo-European Family is generally considered to consist of nine different brunches, which in turn gave rise to daughter languages. Welsh evolved from the Celtic brunch, as did its sister languages - Breton, Cornish, Cumbric, Irish, Scots Gaelic and Manx.
Сornish was a language of people who lived in Britain in the Cornwall inlet and died out towards the end of the eighteenth century. Dorothy Pentreath, who died in 1777, is usually considered to be the last native speaker of Cornish. Manx was spread on the Isle of Man in the Irish Sea, survived until well into the second half of the present sentury and the last native speaker died at the age of 97 in 1974. Other languages are still alive and a lot of people talks on them. But nevertheless all this languages developed from the Celtic language and the people who used this language were the Celts.
The Celts is a group of people who were classified as such by communities who belonged to a separate cultural (and literate) tradition. Celtic area is considered to be the north of Alps and beyond the Mediterranean. It was observers from mediterranean lands of Greece and Rome who called their neighbours Celts. But today scientists ask the question who the Celts really are. The problem of defining what is meant by the terms "Celt" and "Celtic" centres around the relationship, if any, between material culture, ethnicity and language. Judging by archaeology, documentary sources and linguistic material the scientists came to the conclusion that by the last few centuries BC, Celtic territory stretched from Ireland to eastern Europe and beyond, to Galatia (see map). The Celts were technically advanced. They knew how to work with iron, and could make better weapons than the people who used bronze.
Early linguistic evidence for the Celts is extremely rare because northern Europe was non-literate during most of the first millennium BC. When writing was adopted in the Celtic world in the late first millennium it appeared almost entirely in Greek and Latin. Early Celtic evidence consists of inscriptions, coin legends and the names of people and places contained within classical documents.
Now I would like to tell about the Brittonic brunch of Celtic languages, which was spread over the territory of Britain. Because of our knowledge of the Celts is slight, we do not even know for certain how Britain became Celtic. Some scholars think that the Celts invaded Britain, another - that they came peacefully, as a result of the lively trade with Europe about 750 BC on wards. But we know for certain that the language introduced into Britain was similar to that spoken in Gaul (the territory of Celts in Central Europe); indeed, the Celtic speech of Gaul and Britain at the dawn of the historic era can be considered as one language, frequently, referred to as Gallo-Britonic. Three successor languages of Brittonic evolved: Cumbric in southern Scotland and north-west England, Welsh in Wales and Сornish in south-west Britain. The speakers of all three of them were known by their Anglo-Saxon neighbours as Wealas, or Welsh. The word is usually considered to mean foreigner, but it can also mean people who have been Romanized. To describe themselves, the Welsh and the Cumbric speakers adopted the name Cymry and called their language Cymraeg. Cymry comes from the Brittonic combrogi (fellow countryman) and its adoption marks a deepening sense of identity.
It is very interesting to show common and different things between the words of these languages. You can sea these comparison in following table.
Cognate Celtic words
welsh breton Irish gaelic
ty (house) ti teach tight
ci (dog) ki cu cu
du (black) du dubh dubh
cadair (chair) kador kathaoir cathair
gwin (wine) gwin fion fion
You see that almost all words are similar to each other, that’s why they were united in one brunch.