chap - a crack in a lip caused usually by cold

chink - a narrow opening as e.g. between planks in a wall

crevasse - a deep fissure

fatigue crack - a crack in metal resulting from metal fatigue

geological fault, fault, fracture, break, shift - (geology) a crack in the earth's crust resulting from the displacement of one side with respect to the other; "they built it right over a geological fault"

opening, gap - an open or empty space in or between things; "there was a small opening between the trees"; "the explosion made a gap in the wall"

rift - a narrow fissure in rock

slit - a narrow fissure

split - a lengthwise crack in wood; "he inserted the wedge into a split in the log"

volcano, vent - a fissure in the earth's crust (or in the surface of some other planet) through which molten lava and gases erupt

crater, volcanic crater - a bowl-shaped opening at the top of a volcano