1. The concealment or extinguishment of lights that might be visible to enemy aircraft during an air raid.
2. Lack of illumination caused by an electrical power failure.
3. The sudden extinguishment of all stage lights in a theater to indicate the passage of time or to mark the end of an act or a scene.
4. A short, comic vaudeville skit that ends with lights off.
5. A temporary loss of memory or consciousness.
6. A suppression, as of news, by censorhip.
7. Restriction or prohibition of telecasting a sports event in order to ensure ticket sales.
8. The central meaning shared by these nouns is “a temporary loss of consciousness”:
suffers blackouts at high altitudes;
fell in a dead faint at the sight of the cadaver;
sank to the ground in a swoon;
was taken to the emergency room in a state of syncope.