abysm, abyss, aperture, arroyo, blank, box canyon, breach, break, broaching, canyon, cavity, chap, check, chimney, chink, clearing, cleavage, cleft, cleuch, clough, clove, col, coulee, couloir, crack, cranny, crater, crevasse, crevice, cut, cwm, deep, defile, dell, depth, dig, diggings, dike, disclosure, ditch, donga, draw, excavation, fault, fenestra, fissure, fistula, flaw, flume, fontanel, foramen, fracture, furrow, gap, gape, gash, gat, gorge, groove, gulch, gulf, gully, hiatus, hole, hollow, incision, inlet, interval, joint, kloof, lacuna, laying open, leak, mine, moat, notch, nullah, opening, opening up, orifice, outlet, overlook, oversight, pass, passage, passageway, pit, pore, preterition, quarry, ravine, rent, rift, rime, rupture, scissure, seam, shaft, skip, slit, slot, space, split, stoma, throwing open, trench, uncorking, unstopping, valley, void, wadi, well, workings, yawn, yawning abyss