supplementary brief; supplemental document
Used in legal, patent, and official contexts for a document that supplements or amends a previous filing.
It is necessary to submit a supplemental brief to the Patent Office.
The lawyer sent a supplementary document to the court.
意見書 is a written opinion or argument, often used in patent prosecution, whereas 補充書 specifically supplements or amends a previous submission.
Compound of 補充 (supplement, replenish) and 書 (document, writing). The exact historical derivation is uncertain; the term is used in modern legal and patent contexts.