Question

Fly the Coop to escape; to leave suddenly and secretly

Accepted Answer

I tucked my little brother into bed, but the next time I looked, he had flown the coop. A coop is an enclosure or cage for poultry or small animals. If a chicken "flew the coop," it escaped its pen. In the late 1800s and early 1900s "coop" was also a slang word for jail, so this expression often referred to what an escaped prisoner did. Today it is used in connection with any person or animal that secretly escapes or runs away.

Idiom	Fly the Coop
Example	I tucked my little brother into bed, but the next time I looked, he had flown the coop.
Meaning	to escape; to leave suddenly and secretly
Origin	A coop is an enclosure or cage for poultry or small animals. If a chicken "flew the coop," it escaped its pen. In the late 1800s and early 1900s "coop" was also a slang word for jail, so this expression often referred to what an escaped prisoner did. Today it is used in connection with any person or animal that secretly escapes or runs away.

Coop I Secretly Escaped Fly Tucked Brother Bed