expression, ichidan verb
make corrections; correct with a red pen
Literally 'to put in the red brush', referring to the act of correcting or revising a text, often by a teacher or editor. Rare term; more commonly expressed as 朱を入れる or 添削する.
先生が生徒の作文に朱筆を入れる。
The teacher corrects the student's composition with a red pen.
Compound of 朱筆 (red brush) + を (object marker) + 入れる (to put in). The expression originates from the practice of using a red brush or pen to mark corrections on documents.