Creosote

Part of speech: noun (n.)

Wood-tar oil; an oily antiseptic liquid, of a burning smoky taste, colorless when pure, but usually colored yellow or brown by impurity or exposure. It is a complex mixture of various phenols and their ethers, and is obtained by the distillation of wood tar, especially that of beechwood.

Part of speech: verb (v.)

To saturate or impregnate with creosote, as timber, for the prevention of decay.