Charybdis, Maelstrom, abysm, abyss, aperture, arm, armlet, arroyo, back stream, backflow, backwash, backwater, bay, bayou, belt, bight, boca, box canyon, breach, break, broaching, canyon, cave, cavity, chap, chasm, check, chimney, chink, clearing, cleft, cleuch, clough, col, coulee, couloir, countercurrent, counterflow, counterflux, cove, crack, cranny, crater, creek, crevasse, crevice, cut, cwm, deep, defile, dell, depth, dig, diggings, dike, disclosure, ditch, donga, draw, eddy, estuary, euripus, excavation, fault, fenestra, fiord, firth, fissure, fistula, fjord, flaw, flume, fontanel, foramen, fracture, frith, furrow, gap, gape, gash, gat, gorge, groove, gulch, gully, gurge, gut, harbor, hiatus, hole, hollow, incision, inlet, interval, joint, kloof, kyle, lacuna, laying open, leak, loch, lough, maelstrom, mine, moat, mouth, narrow, narrow seas, narrows, natural harbor, notch, nullah, opening, opening up, orifice, outlet, pass, passage, passageway, pit, pore, quarry, ravine, reach, refluence, reflux, regurgitation, rent, rift, rime, road, roads, roadstead, rupture, scissure, seam, separation, shaft, slit, slot, slough, sound, space, split, stoma, strait, straits, swirl, throwing open, trench, twirl, uncorking, unstopping, valley, void, vortex, wadi, well, whirl, whirlpool, workings, yawn, yawning abyss