The six Celtic languages currently spoken are divided into two branches: Goidelic or Gaelic, and Brythonic or British. The former branch consists of Irish, Manx and Scottish Gaelic, while the latter branch includes Welsh, Cornish and Breton. While there are many similarities between the languages in each branch, there are fewer similiarities between the two branches as they have had thousands of years to grow apart.
Differences in spelling and sound changes can disguise related words, but there are quite a few cognates that appear in most or all of the Celtic languages. In some cases the words in one language might be archaic or only used in place names, and more cognates can be found in earlier versions of the the languages. Some words are cognate within each branch of the Celtic languages, but not between the branches.
Words marked with an asterisk are archaic and/or used only in place names. The Cornish words shown are in Common Cornish (Kernewek Kemmyn). The Breton words are in Peurunvan/Modern Standard Spelling.
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Stòr-fhaclan Co-dhàimheil Ceilteach (Database of Celtic cognates)
McBain's Etymological Dictionary of the Gaelic Language