slit
n. countablen. a long, narrow cut or opening in something. You might see a slit in a piece of fabric or a thin opening in a door.
n. a long, narrow incision or opening, typically made by cutting. Refers to both intentional structural gaps and accidental tears.
She looked through the narrow slit in the curtains.
The designer added a long slit to the side of the skirt to allow for easier movement.
Light poured through a thin slit in the heavy oak door, illuminating the dust motes dancing in the hallway.
From Middle English slitten, from Old English slītan, from Proto-Germanic slītaną (“to tear apart”), from Proto-Indo-European (s)leyd- (“to tear, rend (cut apart), split apart”). Possibly cognate with Latin laed- (“to strike, hurt, injure”). Doublet of slite; also related to slice through French borrowing. Apparently unrelated to English slot, whose etymology, however, is uncertain.
Often used with 'in' to describe the location of the opening.