duff
adj. C1 Advanced US //ˈdəf// UK //dˈʌf// duff
adj. broken, useless, or of very poor quality. You use this word when something does not work the way it should.
adj. of poor quality, defective, or useless. Primarily British in register; often used to describe faulty equipment or incorrect information.
I think I bought a duff battery because it won't charge.
The mechanic realized the car wouldn't start because of a duff spark plug that needed replacing.
After hours of troubleshooting the electrical system, the engineer discovered that a single duff connection in the control panel was causing the entire machine to fail.
Usage
Typically used attributively before a noun or predicatively after a linking verb like 'be'.