A thing that fails to work properly or is otherwise unsatisfactory or worthless. The new phone turned out to be a dud, as it stopped working after just a week.
An explosive device that fails to detonate. The bomb squad carefully removed the dud from the construction site.
A person regarded as a failure or disappointment. Everyone expected him to excel, but he turned out to be a dud.
(informal, usually plural) Clothes; garments. He bought some flashy new duds for the party.