Simple categories matching hollow:

• tree,
• bone,
• article,
• object,
• stem,
• structure,
• item,
• polyhedron,
• part,
• jewelry,
• beads,
• organs,
• formation,
• tube,
• passage,
• implement,
• vessel,
• form,
• instrument,
• organ,
• section,
• ware,
• assembly,
• bird,
• needle,
• viscus,
• cavity,
• tubing,
• particle,
• pipe,
• container,
• shell,
• material,
• panel,
• cylinder,
• shaft,
• region,
• animal,
• dish,
• viscera,
• thing,
• area,
• feature,
• product,
• surface,
• tissue,
• glassware,
• ball,
• pole,
• utensil,
• receptacle,
• conduit,
• plant,
• ceiling,
• reed,
• component,
• wall,
• sphere,
• carrier,
• piece,
• space,
• wood,
• body,
• bones,
• fibre,
• handgrip,
• fiber,
• glass,
• shape,
• construction,
• protuberance,

Members with property hollow:

• cup,
• bottle,
• casing,
• neck,
• cabinet,
• pipe,
• saucer,
• wood,
• furnace_tube,
• large_auditorium,
• glove,
• animal_shell,
• carbon_sphere,
• tube,
• bowls,
• stomach,
• trapezoid,
• bushing,
• corporation,
• heart,
• rectangular_form,
• gas,
• tank,
• borosilicate_glass,
• lymphatic_vessel,
• tiled_wallboard,
• fossil_shell,
• inside,
• cooling_pipe,
• container,
• spoon,
• macaw,
• academic_accolade,
• trench,
• table-tennis_ball,
• jar,
• ring,
• automotive_component,
• bark,
• tubing,
• aorta,
• owl,
• kidney_dish,
• kidney,
• porcupine,
• drain,
• thermoplastic_hose,
• leather,
• bladder,
• vessel,
• light_pole,
• doll,
• hi_mouth,
• parrot,
• leaching_gallery,
• vein,
• shoes,
• silica_sphere,
• side_sill,
• airplane_wings,
• bubble_wrap,
• glass_jar,
• chicken_bones,
• long_tube,
• hose,
• cargo,
• gourd,
• cotton,
• capsule,
• gelatin_capsule,
• kettle,
• crack,
• flask,
• eye,
• coffee_pot,
• appendix,
• injection_needle,
• tubular_structure,
• table_plate,
• mask,
• glass_block,
• plasterboard_wall,
• column_cover,
• arbor_leg,
• liver,
• bracelet,
• synthetic-resin_bottle,
• bronchus,
• lung,
• pneumothorax,
• hollow_cone,
• cam_body,
• toy,
• play_ball,
• hat,
• pipe_stem,
• ventilation_slot,
• frontal,
• artery,
• bearing,
• milk_bottle,
• cartridge_shell,
• square,
• boat_hull,
• chassis_part,
• plastic_straw,
• bark_box,
• shampoo_bottle,
• carton,
• polygonal_shape,
• under_eyes,
• tunnel,
• pitcher,
• earring,
• hollow_sphere,
• cartridge_case,
• football,
• rectangle,
• stone_fragment,
• tubular_film,
• gastrointestinal_tract,
• racquetball,
• insect_skeleton,
• automotive_part,
• intestine,
• fiber,
• crockery,
• front_pillar,
• human_organs,
• milk_tube,
• cylinder,
• coil,
• dead_branch,
• mullion,
• automobile_body,
• flexible_endoscope,
• shell,
• bowel,
• urinary_bladder,
• spark-plug_shell,
• hollow_body,
• polyelectrolyte_capsule,
• lid,
• pillar,
• colon,
• sea_shell,
• pvc_pipe,
• large_intestine,
• lotion_bowl,
• cheek,
• cyst,
• small_bowel,
• golf-club_head,
• wall,
• cone,
• vagina,
• wall_void,
• small_vase,
• tissue_forceps,
• baobab,
• cylindrical_form,
• appliance_part,
• speaker,
• microtubule,
• goblet,
• tool_holder,
• cooking_vessel,
• similar_article,
• dog,
• steel_tube,
• dish,
• city,
• plaster,
• trachea,
• circle,
• mast,
• deep_cup,
• table_legs,
• vase,
• pore_size,
• golf-club_shaft,
• spiral_tube,
• hollow_door,
• oval,
• pot,
• basswood,
• pan,
• tibia,
• torso,
• cystic_duct,
• candle_stick,
• alveolus,
• drywall,
• bag,
• ceiling,
• sycamore,
• doughnut_shape,
• missile_casing,
• partition,
• tattoo_tube,
• glass_beads,
• playing_ball,
• plastic_bottle,
• drain_pipe,
• can,
• shoes_boot,
• foam,
• bodywork,
• shelter,
• helmet,
• gut,
• piling,
• ash,
• tub,
• fuel_rack,
• quill,
• pendant,
• abdomen,
• beaker,
• beech,
• rounded_box,
• concave_plate,
• wings,
• chimney,
• stein,
• duodenum,
• cube,
• bubble,
• tubular_component,
• airway,
• roll,
• softball,
• decorative_vessel,
• hand_piece,
• seaplane_body,
• drum,
• canister,
• pig,
• animal_horn,
• oil_tank,
• box_section,
• branch,
• strut,
• flagon,
• cannular_needle,
• urogenital_tract,
• cheekbone,
• radiator_frame,
• hot-water_bottle,
• straw,
• bin,
• syringe_needle,
• ear,
• nose,
• gypsum_wallboard,
• conduit,
• duct,
• dummy,
• pneumatic_cushion,
• capillary,
• oil_drum,
• bronchial_tube,
• renal_pelvis,
• aircraft-engine_component,
• case,
• bones,
• catwalk_framework,
• structure,
• fiberglass,
• jacks,
• pump,
• basketball,
• mirror_head,
• fence_post,
• engine_cradle,
• hypodermic_tubing,
• tile,
• stent,
• boat,
• teapot,
• plate,
• fuel_tank,
• mug,
• catheter,
• valve,
• pore,
• milk_jug,
• plasterboard,
• pillow,
• automobile_stabilizer,
• oxygen_tank,
• gallbladder,
• bowl,
• crate,
• handle,
• bicycle_component,
• pocket,
• sponge,
• horn,
• metal_cylinder,
• coffeepot,
• seminal_vesicle,
• gimbal,
• chicken,
• esophagus,
• dome,
• panel,
• gantry,
• food_canal,
• anaesthetic_bowls,
• storage_box,
• wallboard,
• plastic_tank,
• stove,
• concrete_manhole,
• space_frame,
• glomerulus,
• building,
• attic_space,
• ureter,
• head,
• conveyor_roller,
• human_urethra,
• side_board,
• cage,
• ewer,
• injection_bottle,
• metal_container,
• conical_shell,
• support_post,
• sport_ball,
• brain,
• small_intestine,
• furniture_elements,
• glass_container,
• trash_pit,
• glass,
• gun_tube,
• sexual_gratification,
• circular_tube,
• rubbish_bin,
• doughnut,
• drum_beads,
• sphere,
• solid_disk,
• small_bottle,
• door,
• rubber_glove,
• storage_container,
• biopsy_needle,
• sheetrock,
• reed,
• truncated_cone,
• digestive_tract,
• box,
• ceiling_panel,
• squeaky_toy,
• sugar,
• glasses,
• plastic_pallet,
• hollow_bowls,
• passage,
• funnel,
• jug,
• playground,
• door_handle,
• pressure_vessel,
• adding_stone,
• crucible,
• masonry_chimney,
• room_partition,
• hoop,
• small_shelter,
• cotton_fibre,
• crankshaft_bushing,
• cement_block,
• middle-ear_anatomy,
• lentil_cube,
• bamboo_cane,
• enclosure,
• belly,
• cushion,
• femur,
• bell,
• nuclear_reactor,
• aperture,
• roof,
• envelope,
• urethra,
• table_glass,
• brow,
• metal_gutter,
• sinus,
• oven,
• sinus_cavity,
• windpipe,
• brick,
• doll_head,
• section,
• mold,
• peritoneal_cavity,
• uterus,
• digestive_organs,
• crevice,
• barrels,
• bamboo,
• door_frame,
• cavity,
• storage,
• gastrointestinal_organs,
• pipe_connector,
• reactor,
• jumper,
• pvc,
• concrete_pole,
• organs,
• piano,
• hood,
• soda-pop_bottle,
• table_ware,
• ballpoint_pen,
• suspended_ceiling,
• triangle,
• beads,
• urinary_tract,
• ball,
• tray,
• tankard,
• flute,
• foundry_core,
• hole,
• acrylonitrile_sphere,
• rack,
• aircraft_wings,
• needle,
• jewelry_ring,
• center_pillar,
• pit,
• balloon,
• closed_building,
• teat_cup,
• joint,
• ear_piece,
• steel_shell,
• gravid_uterus,
• lower_bowel,
• rectum,
• pancreas,
• silo,
• frame,
• aluminum_tubing,