slit, crack, aperture, hole, gap
slot
Glen is the word for a long, narrow valley. It traces its origin to 15th century Scottish Gaelic word Gleann.
crack
A door is an opening.
pit
Slim.
Chanelled into a narrow opening.
wide
slit
A crevice is a narrow crack or opening, a fissure or cleft.
A narrow opening can be considered a slit. Narrow openings can be very long or short. There are many different types of narrow openings.
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.
crack!
The Mediterranean
The urethra.