The determination of how long ago different languages evolved from a common source language: Glottochronology is the application of statistics to vocabulary in order to determine the degree of relationships between two or more languages and the time of their splitting off from a common ancestor.

lottochronology is the branch of lexicostatistics that studies the rate of the replacement of vocabulary and attempts to determine what percentage of basic vocabulary two presently distinct, but related languages share by using the information that is obtained to estimate how long ago they ceased being a single language.