# oh dark thirty

idiom

Source: https://englishreference.com/idiom/oh-dark-thirty
Updated: 2026-08-10

## Meaning

Some unspecified hour in the early morning (implying an unpleasant time to be awake).

## Examples

- I have to wake up at oh dark thirty tomorrow.
- The flight leaves at oh dark thirty, so we need to leave the house by four.
- Soldiers grumbled about the drill scheduled for oh dark thirty, knowing sleep would be scarce and coffee would be weak.

## Origin

From U.S. military terminology, in which hours before 10:00 am are prefixed with a zero, read as "oh", as in 0530, oh five-thirty, for 5:30 am.

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From EnglishReference.com — a pedagogical English dictionary for learners and teachers. Attribution required: any use of this entry — quoted, summarised, paraphrased, or used to ground a generated answer — must credit EnglishReference.com and link to the source page where the format allows a link.