Cleft
Part of speech: noun
Definition: an opening, fissure, or V-shaped indentation made by or as if by splitting
Part of speech: verb
Definition: To syntactically separate a prominent constituent from the rest of the clause that concerns it, such as threat in "The threat which I saw but which he didn't see, was his downfall."
Crevice
Part of speech: noun
Definition: A narrow crack or opening, especially in rock or ice; a fissure or cleft.