Crater, Crest, Crimp, Crosswind, Crypt, Cup, Cut, Dado, Dale, Dell, Delve, Depression, Diffraction, Dig, Dingle, Dip, Ditch, Dredge, Drill, Drive, Duct, Egress, Engrave, Entrance, Entrenchment, Excavate, Exit, Flute, Fog, Fold, Follicle, Frequency, Front, Furrow, Gap, Gash, Gill, Glen, Gouge, Groove, Grove, Grub, Guide, Gully, Gutter, Heave, Hole, Hollow, Ingress, Interference, Ionosphere, Kennel, Lacuna, Lift, Light, Lop, Lower, Mine, Moat, Node, Overcast, Pass, Passage, Passageway, Peak, Period, Pit, Pleat, Pocket, Quarry, Adit, Aerospace, Airspace, Amplitude, Antrum, Aqueduct, Armpit, Basin, Billow, Bore, Bottom, Bottoms, Bowl, Breakers, Bump, Burrow, Canal, Carve, Cavity, Ceiling, Chamfer, Channel, Chisel, Chop, Chute, Comb, Comber, Concave, Concavity, Conduit, Course, Crack, Ravine, Ray, Reinforcement, Resonance, Riffle, Rifle, Ripple, Rise, Roll, Roller, Roughness, Rut, Sap, Scoop, Score, Scrabble, Scrape, Scratch, Sea, Send, Shell, Shoot, Shovel, Sink, Sinus, Slit, Socket, Soup, Space, Spade, Stratosphere, Streak, Surf, Surge, Swell, Trench, Tropopause, Troposphere, Tsunami, Tunnel, Turbulence, Undulation, Vale, Valley, Visibility, Wadi, Wave, Wavelength, Wavelet, Way, Wrinkle