danger
n. C / Un. the possibility that someone will be harmed or killed. It can also mean a person or thing that is likely to cause trouble or harm.
n. the possibility of suffering harm or injury; a person or thing likely to cause harm or injury.
The sign warns people about the danger of falling rocks.
Firefighters often put their lives in danger to save people trapped inside burning buildings.
The primary danger of the current economic policy lies in its failure to address the widening gap between urban and rural infrastructure development.
From Middle English daunger (“power, dominion, peril”), from Anglo-Norman dangier, from Old French dangier, alteration of Old French dongier (due to association with Latin damnum (“damage”)) from Vulgar Latin *dominārium (“authority, power”) from Latin dominus (“lord, master”). Displaced native Old English frēcennes.
Uncountable when referring to the general state of being at risk; countable when referring to specific threats or hazards.
He is in a dangerHe is in dangerWhen used in the fixed phrase 'in danger' to describe a state of risk, the noun is uncountable and does not take an article.