a brake operated by hand; usually operates by mechanical linkage
"The driver had to manually operate the emergency brake because the automatic system failed while descending the steep hill."
A situation which poses an immediate risk and which requires urgent attention.
"The pilot declared a medical emergency after one passenger collapsed in the aisle."
In plain English: An emergency is a sudden and serious problem that needs immediate help.
"We have to call an emergency number if someone is in serious danger."
Usage: Use "emergency" to describe any sudden crisis that demands immediate action or special care, such as a medical accident or natural disaster. It refers specifically to the dangerous situation itself rather than the plan to handle it, which is called an "emergency procedure."
The word emergency comes from the Medieval Latin emergentia, which is derived from the Latin verb meaning "to emerge" or "arise." It entered English as a doublet of emergence, originally referring to something that has come forth into view.