lost book; missing book
Refers to a book or written work that has been lost or is no longer extant, often used in historical or bibliographic discussions.
The contents of that lost book are partially known from later citations.
Variant kanji form using 佚 instead of 逸; less common but still encountered in bibliographic contexts.
Compound of 逸 (lost, missing) and 書 (book, document). The exact historical derivation is uncertain; the spelling is conventionally associated with the meaning of a lost written work.