"slit opening" is correct and usable in written English.
It can be used to describe a narrow opening, such as a hole or crack. For example, "The rat squeezed through the tiny slit opening in the wall."
The silhouette was mostly long and slender, but with inserts of a heavier texture at one breast, a slit opening up the spine, split skirts or a sudden gleam of silver like moonlight on water.
The discrete element method (DEM) is used to predict the properties of a particle curtain created by the three-dimensional granular flow through a hopper constricted by a slit opening.
This will reinforce both your long seam as well as the top of the slit opening.
One, Babu Bajrangi, boasted of how he slit open the womb of a pregnant woman.
He fished out his car keys, slit open the box, and removed the microtubes.
When he returned, he slit open the cellophane and gently pulled a test book from its wrapping.
Silva made it double figures in the 89th minute after another move that slit open the Tahiti defence.
You slit open the belly, tug out the guts, strip naked, crawl inside, read a little light fiction for a while, and nod off.
Every few weeks, as a new shipment of books arrived at each of our different addresses, Susan, Maureen, and I slit open the carton and said to ourselves, Please, let this box contain the One.
For years she'd snooped in Kay-Kay's life, read her diary, slit open the seams of her coat, turned over the dresser drawers, shoved a hand between the mattress and the box spring.
They are not nearly as bad as in London or Rome, but they can slit open your backpack on the subway and take your purse or wallet before you know it.
