Before revision: When a word in one language is similar to a word in another, one potential explanation for the similarity is that the word was borrowed by one language from the other, or that both borrowed it from some third source.
After revision: Role of borrowing in historical linguisticsWhen a word in one language is similar to a word in another, one potential explanation for the similarity is that the word was borrowed by one language from the other, or that both borrowed it from some third source.