devoted scholar; diligent student
A somewhat literary or formal term for a person deeply committed to learning. Not an everyday casual word; more likely in written descriptions or elevated speech.
He is truly a person worthy of being called a devoted scholar.
In the study of this man, known as a diligent student, books from all ages and countries are lined up.
勉強家 is a common word for a hard-working student or someone who studies a lot. 篤学の士 is more formal and implies a deeper, almost scholarly dedication.
Composed of 篤学 (devoted to learning) + の (possessive particle) + 士 (person of a certain quality). The exact historical origin is uncertain, but it follows a classical Chinese-derived pattern for describing a person of virtue or skill.