Cognate
Etymology
From Latin cognatus, "related by blood," from co- ("together") + gnatus, an old form of natus ("born"), from nasci ("to be born"). The word was originally about kinship among people. Comparative linguists borrowed that family metaphor for words: cognates are words "born together," descended from one ancestral form.
noun · /KOG-nayt/
A word that shares a common ancestor with a word in another language, showing a family resemblance.
What it names
The genetic likeness between languages — why "night," German Nacht, and Latin nox visibly descend from the same distant word.
Example
Spanish learners lean on cognates like "familia" and "importante" — until a false friend like "embarazada," meaning pregnant, trips them up.
Related idea
True cognates share an ancestor; a loanword is passed sideways between languages rather than inherited. English "beef" and French "boeuf" look like cognates but "beef" is actually a loanword from French.