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 in comparing a standardized set of wordlists 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.
Lexical similarity can be used to evaluate the degree of genetic relationship between two languages. Percentages higher than 85% usually indicate that the two languages being compared are likely to be related dialects.
The lexical similarity is only one indication of the mutual intelligibility of the two languages, since the latter also depends on the degree of phonetical, morphological, and syntactical similarity. It is worth noting that the variations due to differing wordlists weigh on this. For example, lexical similarity between French and English is considerable in lexical fields relating to culture, whereas their similarity is smaller as far as basic (function) words are concerned. Unlike mutual intelligibility, lexical similarity can only be symmetrical.
Indo-European languages 
|Lexical similarity coefficients|
|Language 2 →||eng||fra||deu||ita||por||ron||roh||rus||srd||spa|
- Language codes are from standard ISO 639-3.
- Ethnologue does not specify for which Sardinian variety the lexical similarity was calculated.
- "-" denotes that comparison data are not available.
- Ethnologue.com (lexical similarity values available at some of the individual language entries)
- Definition of lexical similarity at Ethnologue.com
- Rensch, Calvin R. 1992. "Calculating lexical similarity." In Eugene H. Casad (ed.), Windows on bilingualism , 13-15. (Summer Institute of Linguistics and the University of Texas at Arlington Publications in Linguistics, 110). Dallas: Summer Institute of Linguistics and the University of Texas at Arlington.
- See, for instance, lexical similarity data for French, German, English