These words refer to a small gap or opening in a surface. Crack suggests an opening longer than wide, and may refer to a normal opening or to one formed by force, violence or some malfunction: the crack under the door; faint cracks running through the whole base of the pillar; putting his eye to a crack in the partition. While crack may or may not suggest an opening through which light or air might pass, chink invariably suggests such an opening: the unfilled chinks between the logs forming the cabin wall; a chink in the dike through which water had begun to seep.

Breach suggests a gap in something that might impair its functioning and made, usually, by wear or some sundering force: a breach but by the enemy through our front lines, leaving headquarters vulnerable to attack. It may refer as well to any natural gap of any size or shape in the distribution of items forming a group: a breach in the row of trees that widened out finally into a path. Cleft , by contrast, most commonly suggests a natural indentation in something: a cleft in his chin; in the cleft of a tree. It may also suggest something formed by wear or force: a bird perching where the lightning had made a cleft in the rock. In no case does the word suggest an opening clear through to the other side of something, as is true of chink .

Crevice and fissure both usually refer to long cracks formed by natural forces at work in a terrain. Crevice most commonly suggests a crack in an incline or hillside: a mountaineer moving sure-footedly from crevice to crevice in the mountain face. Fissure , by contrast, suggests a long slit like opening in a more level surface: fissures in the ground formed by the earthquake; stretches of snow that tremored and broke open in fissures at every step he took. Crevice can also be applied outside this context: crevices between the bricks deep enough for him to gain a toe-hole in the wall; using putty to fill the crevices in the woodwork and spackle to seal up the small cracks in the wall.