The phrase "in danger" refers to a state of vulnerability or risk, where there is a possibility of harm, injury or even death. There are several synonyms that can be used in place of "in danger" such as endangered, at risk, under threat, imperiled, in peril, under siege, in jeopardy, and precarious.
Endangered is commonly used in situations where there is a risk of extinction of certain animals or species. At risk is another phrase used to refer to something that is in danger or susceptible to harm. Under threat is a phrase used for situations where there is a possibility of danger, such as a city or country being under threat of attack. In peril, under siege and in jeopardy are other expressions that highlight the seriousness of a situation when there is significant danger to life, health or property.