boron: a trivalent metalloid element; occurs both in a hard black crystal and in the form of a yellow or brown powder
chemical element: any of the more than 100 known substances (of which 92 occur naturally) that cannot be separated into simpler substances and that singly or in combination constitute all matter
lignin: a complex polymer; the chief constituent of wood other than carbohydrates; binds to cellulose fibers to harden and strengthen cell walls of plants