Abyss, Antrum, Aperture, Armpit, Basin, Booth, Bowl, Box, Breach, Break, Broaching, Canyon, Cell, Chamber, Chap, Chasm, Check, Chimney, Chink, Clearing, Cleft, Col, Compartment, Concave, Concavity, Couloir, Crack, Cranny, Crater, Crevasse, Crevice, Crib, Crypt, Cup, Cut, Deep, Defile, Dell, Depression, Depth, Dip, Disclosure, Ditch, Donga, Draw, Excavation, Fault, Fissure, Fistula, Flaw, Fold, Follicle, Fontanel, Foramen, Fracture, Furrow, Gap, Gape, Gash, Gorge, Groove, Gulf, Gully, Hiatus, Hold, Hole, Hollow, Incision, Inlet, Interval, Joint, Kloof, Lacuna, Leak, Manger, Moat, Notch, Opening, Orifice, Outlet, Pass, Passage, Passageway, Pew, Pit, Pocket, Pore, Ravine, Rent, Rift, Rime, Rupture, Scoop, Seam, Shaft, Shell, Sink, Sinus, Slit, Slot, Socket, Space, Split, Stall, Stoma, Trench, Trough, Vacuity, Valley, Vault, Void, Wadi, Well, Yawn