Dud

A dud is in general something that fails to function in the way it is intended to. In a military context the word is often used to refer to an ammunition round or explosive that fails to fire or detonate as expected. Poorly designed devices, have higher chances of being duds. They must be deactivated and disposed of carefully. In war-torn areas, many curious children have been injured or killed from tampering with such devices.
The variation absolute dud describes a nuclear weapon that fails to explode.

Etymology

The term descends from the Middle English dudde, originally meaning worn-out or ragged clothing, and is a cognate of duds and dowdy. Eventually dud became a general pejorative for something useless, including ammunition. The word's use is attested from 1355.