(idiomatic) Some unspecified hour in the early morning (implies an unpleasant time to be awake)

Alternative spelling of oh dark thirty

Dark matter traveling at relativistic speeds, less than ultra-relativistic particles, but more than classical particles.

Dark matter traveling at ultra-relativistic velocities

Dark matter traveling at classical, non-relativistic speeds

A big, bright orange and black butterfly with a greenish body, Argynnis aglaja, of the family Nymphalidae

plural of dark green fritillary

(informal) The wee hours.

(chiefly US military slang) An otherwise unspecified time of night; some time when it is dark out.

(chiefly US military slang) Half an hour past 12(am) midnight, or more formal and exact would be 00:30; The practice of adding “dark” and “thirty” (30) can be used sometimes as a slang term in place of an otherwise specific time a time of night, meaning some time when it is dark out between 00:01 - 05:00 hours local time.