How did Samuel Johnson’s definition of internecine help change the word’s meaning?

Samuel Johnson’s definition of internecine in his 1755 A Dictionary of the English Language significantly altered the word's meaning through a lexicographical error.1

Originally, internecine derived from the Latin internecinus and meant "deadly" or "marked by great slaughter". When Johnson defined the term as "endeavouring mutual destruction," he mistakenly assumed the prefix inter- signified "mutual" or "reciprocal," rather than its actual function in this context of indicating the completion of an action.21

Because Johnson’s dictionary was highly influential and served as a standard for over a century, subsequent dictionaries adopted his definition. This caused the sense of "mutual" to become the dominant meaning of the word. By the 20th century, this shift further evolved to associate the term with internal group conflict, which remains its most common usage today.132