本
ホン, もと, まと, ごう
book, present, main, origin, true, real, counter for long cylindrical things
JLPT5 G1 S5 F10
木 tree/wood + a horizontal line# (compare that in 旦) indicating the *base*/*root* of the trunk → *origin*; *originally*; *true*; *one's own*; *capital*; *counter* (for cylindrical objects) → *book* (← counter for scrolls ← counter for cylindrical objects).
[Full Kanji Etymology List]