1. 不中用的;失灵的;出故障的
Dud means not working properly or not successful.

1. an event that fails badly or is totally ineffectual

e.g. the first experiment was a real turkey
the meeting was a dud as far as new business was concerned

Synonym: turkeybomb

2. an explosion that fails to occur

Synonym: misfire

3. someone who is unsuccessful

Synonym: flopwashout