本質
ほんしつ · honshitsu · JLPT N1 · noun
kernel
本 = root/origin + 質 = substance: the root substance of a thing, its true nature
本 means root or origin, and 質 means substance or quality. Together they name what a thing is at its root, beneath its surface traits and appearances.
本 — tree 木 + mark at base
本 is a pictograph of a tree (木) with a stroke at its base, marking the roots. From this 'root' meaning it extended to 'origin,' 'source,' and 'foundation.' In modern usage it also serves as a measure word for bound objects like books.