What is the X in X-mas?
c.1825, "person in ragged clothing," from duds (q.v.). Sense extended by 1897 to "counterfeit thing," and 1908 to "useless, inefficient person or thing." This led naturally in World War I to "shell which fails to explode," and thence to "expensive failure."
c.1300, dudde "cloak, mantle," later in plural, "ragged clothing" (1560s), of uncertain origin.
: a dud bombnoun
Clothing; threads: To see them washed and put in and out of their duds was perhaps the greatest pleasure of her life
[1300+; origin unknown; perhaps fr one or another English or Celtic words meaning ''cloth, rag'']