Swadesh list in the context of Glottochronology

In linguistics, lexical similarity is a measure of the degree to which the word sets of two given languages are similar. A lexical similarity of 1 (or 100%) would mean a total overlap between vocabularies, whereas 0 means there are no common words.

There are different ways to define the lexical similarity and the results vary accordingly. For example, Ethnologue's method of calculation consists of comparing a regionally standardized wordlist (comparable to the Swadesh list) and counting those forms that show similarity in both form and meaning. Using such a method, English was evaluated to have a lexical similarity of 60% with German and 27% with French.

Morris Swadesh (/ˈswɑːdɛʃ/ SWAH-desh; January 22, 1909 – July 20, 1967) was an American linguist who specialized in comparative and historical linguistics, and developed his mature career at UNAM in Mexico. Swadesh was born in Massachusetts to Bessarabian Jewish immigrant parents. He completed bachelor's and master's degrees at the University of Chicago, studying under Edward Sapir, and then followed Sapir to Yale University where he completed a Ph.D. in 1933. Swadesh taught at the University of Wisconsin–Madison from 1937 to 1939, and then during World War II worked on projects with the United States Army and Office of Strategic Services. He became a professor at the City College of New York after the war's end, but was fired in 1949 due to his membership in the Communist Party. He spent most of the rest of his life teaching in Mexico and Canada.

Swadesh had a particular interest in the indigenous languages of the Americas, and conducted extensive fieldwork throughout North America. He was one of the pioneers of glottochronology and lexicostatistics, and is known for his creation of the Swadesh list, a compilation of basic concepts believed to present across cultures and thus suitable for cross-linguistic comparison. Swadesh believed that his techniques could discover deep relationships between apparently unrelated languages, thus allowing for the identification of macrofamilies and possibly even a "Proto-Human" language. His theories were often controversial, and some have been deprecated by later linguists.