本体
ほんたい · hontai · JLPT N1 · noun
trunk
本 (root, base) + 体 (body) = the base body of a thing: its substance, the trunk of it
Compound of 本 (origin, root, base) and 体 (body). The 'base body' is the core substance a thing is built on, like a tree's trunk holding up its branches.
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.