something that fails to perform as it should; a bomb, missile, etc that fails to explode
a counterfeit or fake
a weak, spiritless, or ineffectual person
(in pl) clothes
(sense 4) Middle English dudde coarse cloak; earlier history unknown. (senses 1,2,3) and dud2 may have evolved via a 16th-cent. meaning ‘rags, tatters’, or may be a different word of unknown origin