knob
nounUK /nɒb/
US /nɑːb/
A round handle you turn to open a door or make something work.
She turned the knob to open the door.
OTHER MEANINGS
2. A small round lump or bump on a surface.
The tree trunk had a big knob on its side.
3. A small amount of butter.
He added a knob of butter to the pan.
4. A rounded control on a machine or device.
Turn the volume knob to make the music louder.