Definition - The study of the rate of language change.
Note: For a more detailed definition, see the OED citation below.

Etymology -
The term was coined by combining the Greek glossa, tongue, with chronology, which derives from the Greek khronos, time.

Oxford English Dictionary -
Its first citation is from 1953:
"Glottochronology, a technique for inferring, from statistical comparisons of language systems, estimates not only of their probable familial relationships but also of the dates when the branches of a language family broke off from one another and from the parent language."
(J. B. Carroll Study of Lang. ii. 62)

Quotation -
"Glottochronology [is] the attempt to estimate how long ago two languages separated from a common ancestor by evaluating their degree of divergence on a list of key words."
(Source: 1491: New Revelations of the Americas Before Columbus, Charles Mann (P 41))

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