I have not been able to track down exactly how or when the German prefix invaded the English language. It translates as "characteristic," and what we call "eigenvalues" were called "characteristic values" in old texts. More rarely they were called "proper values," following French terminology. It is useful to have a simple technical prefix to designate eigenvalues, eigenvectors, eigenfunctions, etc., but linguists would rightly argue that such words are neither Fisch nor Fowler.

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