General
zero dark thirty
What does zero dark thirty mean?
A humorous way to describe an unspecified, unpleasantly early hour of the morning when one has to be awake. Often pronounced 'oh dark thirty.'
"We're rolling out at zero dark thirty, so get some sleep."
Origin
US military slang, from 24-hour time ('zero' hundred hours) plus a vague 'thirty.'
Frequently asked questions
What does 'zero dark thirty' mean?
It's a humorous term for an unspecified, unpleasantly early hour of the pre-dawn morning when you have to be awake.
Is there an actual time that is 'zero dark thirty'?
No — it's deliberately vague. It plays on 24-hour military time ('zero hundred hours') plus an invented 'thirty' to mean simply 'very, very early.'
Why is it also said as 'oh dark thirty'?
Because in military time-speak the leading zero is often pronounced 'oh,' so 'zero dark thirty' and 'oh dark thirty' are the same phrase.
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