Ditto, in footnotes

IDEM

This Latin term often appears in bibliographies to mean "the same author" as the previous citation.

The clue plays on the Latin term used in footnotes to mean "the same" or "likewise." "Ditto" is a casual way to say the same thing, and in formal writing, "idem" serves that exact purpose—it’s the Latin equivalent. The answer isn’t a direct translation but a precise match for how scholars repeat a citation or reference without rewriting it. Think of it as the academic version of saying "same as above."