Whatsit (noun)

A thing or device whose name is not known or has been forgotten.

Origin:

Informal, origin unknown.

Examples:

1. I have no idea what that whatsit is, but it looks like it needs batteries.
2. I can"t remember the name of that whatsit, but it"s the one that you twist to open.
3. I can't find the whatsit that goes on the end of this hose.
4. I don't know what you call it but the whatsit that holds the wheel on the car.
5. This is the whatsit you use to change the oil in your car.