What does idem mean?
Idem is a formal word meaning “the same as what has just been mentioned.” It is used particularly in legal writing, bibliographies, citations, and other formal reference systems where repetition would be unnecessary. In a sequence of references, idem indicates that the next source is identical to the preceding one; it can therefore function as a compact alternative to writing “same as above” or repeating the source in full. Although the word is now uncommon in general conversation, it remains useful in specialist and scholarly prose because it is exact, concise, and established. Its Latin origin gives it a particularly formal character, and readers may encounter it in legal documents, academic notes, catalogues, and historical reference lists. The expression should not be confused with “i.e.,” which introduces an explanation rather than identifying the preceding item.
The same as the immediately preceding item or wording.
"The discussion on page 40 continues here, idem."
Chiefly formal, legal, or bibliographic; less common in ordinary speech.
Something that is the same as the item immediately preceding it; an identical reference or wording.
"The catalogue lists the edition twice, the second entry being an idem."
Rare and chiefly found in formal or legal reference contexts.
Rare; usually avoided by repeating the relevant reference or using an elliptical construction.
"The appendix includes several idems of the earlier entries."
In legal writing, idem is a precise shortcut for saying that a reference is exactly the same as the one before it.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does idem come from?
The English word comes directly from Latin idem, meaning “the same.” Latin idem was formed from id, meaning “the same,” and the demonstrative particle -em. English speakers borrowed the word for use in formal citation and reference traditions, where it could stand for an identical repeated item without restating it.
How idem is actually used
This is formal, literary, and especially legal in register. It is more common in legal and scholarly contexts than in everyday speech.
Easily confused with idem
“Idem” means “the same as the preceding item,” whereas “i.e.” means “that is” and introduces an explanation or restatement.