Definition - Words that shares the same ancestor.

Example -
Some Indo-European cognates of the English word night are (all of them derive from the Proto-Indo-European *nokt, night):

Nacht (German),
natt (Swedish),
noc (Czech),
nyx (Greek),
nox (Latin), and
nakt (Sanskrit).

Etymology -
The word derives from the Latin com, together + gnatus, born.

Oxford English Dictionary -
Its first citation in this sense is from 1827:
"A cognate language."
(G. Higgins Celtic Druids 61)

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