noun
headnote; marginal note; annotation at the top of a page
Refers to a note or comment placed at the top of a page or in the margin, often in scholarly or literary works.
この本の頭注には、難しい言葉の説明が書いてある。
The headnotes in this book explain difficult words.
古文の教科書には、よく頭注がついている。
Classical Japanese textbooks often have marginal notes.
Compound of 頭 (head, top) and 注 (annotation, note). The spelling 頭註 uses the older form 註 for 'note'.