Definition of "dud"

The only amusing highlight was Gudgeon having managed to exploit U.S. codebreaking efforts to ambush and destroy the submarine I-173, albeit not for the lack of the Mark 14's trying to sabotage the effort, as the torpedo that had hit the sub had refused to detonate; it seemed, however, that the car-crash levels of kinetic energy involved in the dud simply ramming the sub had nonetheless done enough to fatally damage it.

2021 December 29, Drachinifel, 21:03 from the start, in The USN Pacific Submarine Campaign - The Dark Year (Dec'41 - Dec'42)‎, archived from the original on 19 July 2022

At the end of the day, the vast majority of primary schools are vibrant, friendly places and you may struggle to choose one because they all seem so great. Primary schools tend to have the feelgood factor. If you just aren't feeling it, this one's probably a dud.

2014 September 23, A teacher, “Choosing a primary school: a teacher's guide for parents”, in The Guardian