The term "weapon slit" refers to a narrow opening or cut in a weapon used for a specific purpose. Some synonyms for the term might include "weapon notch," "weapon groove," or "weapon channel." All of these synonyms convey a similar sense of a narrow space or groove in a weapon that serves a specific function. Other possible synonyms might include "weapon aperture," "weapon hole," or "weapon groove." Ultimately, the most appropriate synonym for "weapon slit" will depend on the context in which it is being used and the specific connotations or nuances that the writer wishes to convey with the term.