What is "billethead"

Billethead \Bil"let*head`\ (b[i^]l"l[e^]t*h[e^]d), n. (Naut.) A round piece of timber at the bow or stern of a whaleboat, around which the harpoon line is run out when the whale darts off.

n. (context nautical English) A round piece of timber at the bow or stern of a whaleboat, around which the harpoon line is run out when the whale darts off.