deadwood; useless wood
Refers to wood from a tree that is considered worthless for construction or crafting. The term is literary and not used in everyday conversation.
Deadwood is useless as a building material.
useless person; good-for-nothing
Humble expression used to refer to oneself or one's own group as incompetent or worthless. It is self-deprecating and not used to describe others directly. This usage is rare and literary.
A useless person like me is not fit for that job.
From Chinese 樗材 (chūcái), literally 'Ailanthus wood', a tree whose wood is considered useless, hence metaphorically a useless person. The Japanese reading ちょざい is the on'yomi of the characters.