concealedknob
nounUK /kənˈsiːld nɒb/
US /kənˈsiːld nɑːb/
A knob that is hidden so you can barely see it.
She found the concealedknob behind the picture frame and opened the secret door.
OTHER MEANINGS
2. A small hidden bump or lump on a surface.
The frog's skin had a concealedknob that helped it blend in.
3. A secret control used to unlock something.
The spy turned the concealedknob to reveal the hidden compartment.
4. A hidden rounded part on a machine or tool.
He pressed the concealedknob to start the old clock.