dud
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unexploded ordnance
A bomb, grenade, or other explosive device that did not explode as intended after being dropped or fired.
Die Baustelle musste evakuiert werden, nachdem ein Blindgänger aus dem Zweiten Weltkrieg gefunden wurde.
The construction site had to be evacuated after unexploded ordnance from the Second World War was found.
dud
Colloquial and derogatory for a person who is incompetent, unsuccessful, or useless; a failure.
Der neue Stürmer entpuppte sich leider als totaler Blindgänger und hat noch kein einziges Tor geschossen.
Unfortunately, the new striker turned out to be a total dud and hasn't scored a single goal yet.
flop
Colloquial for a plan, idea, or product that fails completely or turns out to be worthless.
Die teure Werbekampagne war ein finanzieller Blindgänger und brachte keine neuen Kunden.
The expensive advertising campaign was a financial flop and brought in no new customers.
The word is made up of 'blind' and 'Gänger' (from 'gehen', to go). Here, 'blind' means 'not functioning.' A 'Blindgänger' is therefore literally something that 'goes' (e.g., flies) but 'blindly' misses its target, meaning it does not work.
Die Granate war zum Glück ein Blindgänger.
Luckily, the grenade was a dud.
You can recognize the literal meaning (m01) from words like 'Bombe' (bomb), 'Krieg' (war), 'Baustelle' (construction site), or 'entschärfen' (to defuse). The figurative meanings (m02, m03) colloquially refer to people, projects, or ideas that fail.
Bei den Bauarbeiten wurde ein alter Blindgänger entdeckt.
An old unexploded bomb was discovered during the construction work.
When a person is called a 'Blindgänger' (dud), it is very colloquial and a strong insult. It means that the person is considered completely incompetent or useless.
Nenn deinen Kollegen nicht Blindgänger, das ist wirklich verletzend.
Don't call your colleague a dud; that's really hurtful.
In connection with unexploded bombs, the verbs 'finden' (to find), 'bergen' (to recover), 'entschärfen' (to defuse), or 'sprengen' (to detonate) are often used.
Ein Spezialteam muss den Blindgänger entschärfen.
A specialist team has to defuse the unexploded ordnance.
For the figurative meaning, the phrases 'sich als Blindgänger erweisen' (to prove to be a dud) or 'sich als Blindgänger entpuppen' (to turn out to be a dud) are very typical. They express that someone or something later turns out to be a failure.
Der hochgelobte Neuzugang hat sich leider als Blindgänger erwiesen.
Unfortunately, the highly praised new signing proved to be a dud.
loser / dud
A Versager can generally be a projectile or mechanism that does not work as intended. A Blindgänger is more specifically an explosive device that failed to detonate. Versager is appropriate for another kind of technical malfunction, while Blindgänger is appropriate when the explosion failed to occur.
Das Geschoss explodierte nach dem Abschuss nicht und war ein Blindgänger.
The projectile did not explode after it was fired, so it was a dud.
Das Geschoss war wegen seiner defekten Steuerung ein Versager.
Because of its faulty guidance system, the projectile was a dud.
