Magnum opus and Textbook

Magnum opus noun - Something (as a work of art) that is a great achievement and often its creator's greatest achievement.

Textbook and magnum opus are semantically related. In some cases you can use "Textbook" instead a noun phrase "Magnum opus".

Textbook noun - A book used for instruction in a subject.

Magnum opus and textbook are semantically related. Sometimes you can use "Magnum opus" instead a noun "Textbook".