Well I'm not entirely sure but I think it's a small narrow cut.
Volcanoes occur in long, narrow belts because that's were the pate boundaries are.
Fault
Ria is a long narrow inlet.
misericorde - a long, narrow knife
A long narrow and very deep canyon where the ocean floor bends down toward the mantle is called an ocean trench. This is caused by two plates pulling apart.
A narrow opening can be considered a slit. Narrow openings can be very long or short. There are many different types of narrow openings.
crack!
wide
slit
Slot
The pharynx is the narrow opening at the back of the mouth. It is part of both the digestive system and the respiratory system.
spinal cord
The shape of the opening. A Beaker has a wide opening, the curved sides of the beaker do not converge. A flask has a narrow opening, the curved sides form a narrow neck, that can be bunged.
Chanelled into a narrow opening.
The Mediterranean
The urethra.
Nozzle