burn the midnight oil
To stay awake late at night to work or study: “Jill has been burning the midnight oil lately; I guess she has a big exam coming up.”
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Words nearby burn the midnight oil
Idioms and Phrases with burn the midnight oil
Stay up late working or studying, as in The semester is almost over and we're all burning the midnight oil before exams. This expression alludes to the oil in oil lamps. [Early 1600s]