Crack of dawn and Sunup

Sunup and crack of dawn are semantically related in dawn topic. In some cases you can use "Sunup" instead a noun phrase "Crack of dawn", when it comes to topics like daybreak, first light, beginning of day, beginning of light hours.

Sunup noun - The first appearance of light in the morning or the time of its appearance.

Crack of dawn and sunup are semantically related in dawn topic. You can use "Crack of dawn" instead a noun "Sunup".