Synonyms:
* Day: This is the most common synonym.
* Daytime hours: This is a more formal way of saying daytime.
* Sunlight hours: This emphasizes the presence of sunlight.
* Daybreak: This refers to the beginning of the day.
* Broad daylight: This emphasizes that it is not nighttime.
Antonyms:
* Night: This is the most common antonym.
* Nighttime: This emphasizes the period of darkness.
* Darkness: This emphasizes the absence of light.
* Nightfall: This refers to the beginning of the night.
* Midnight: This refers to the middle of the night.
The best synonym or antonym to use will depend on the specific context.