Simple categories matching opaque:

• material,
• bag,
• plastic,
• object,
• filler,
• sack,
• solid,
• foodstuff,
• adhesive,
• gemstone,
• liquid,
• glass,
• surface,
• sunscreen,
• stone,
• part,
• content,
• paint,
• obstacle,
• assembly,
• mark,
• fence,
• coating,
• paper,
• article,
• matter,
• contaminant,
• sheet,
• matrix,
• substrate,
• container,
• fiber,
• medium,
• barrier,
• substance,
• ink,
• oxide,
• web,
• fluid,
• ingredient,
• original,
• aggregate,
• tissue,
• layer,
• fabric,
• copy,
• structure,
• conductor,
• cell,
• symbol,
• item,
• system,
• language,
• film,
• metal,
• beverage,
• particle,
• rock,
• picture,
• document,
• mineral,
• product,
• imperfection,
• obstruction,
• body,
• component,
• pigment,
• creature,
• gem,
• powder,
• image,

Members with property opaque:

• fog,
• photographic_print,
• peat,
• metal,
• wood,
• metallic_foil,
• white_paint,
• asphalt,
• paper,
• malachite,
• wall,
• turquoise,
• jade,
• au,
• sail_cloth,
• iron_oxide,
• dark_canvas,
• paint,
• armored_steel,
• heavy_cotton,
• knapsack,
• sound,
• ink,
• stamp,
• air,
• carbon-black_pigment,
• cream,
• camera,
• opal,
• onyx,
• ruler,
• matrix,
• nickel,
• milk,
• stone,
• primer,
• ivory,
• cashmere,
• carton,
• milk_jug,
• micro_card,
• cartilage,
• bentonite,
• keg,
• muddy_water,
• jewelry,
• asphalt_paper,
• plastic_tarp,
• emulsion,
• plant,
• pt,
• fog_layer,
• graphite,
• colloid,
• clay,
• envelope,
• pyrrhotite,
• semigloss,
• spleen,
• metallic_powder,
• food_container,
• model,
• map,
• agar,
• pe_bottle,
• clothing_fabric,
• footlocker,
• silver_grain,
• cassiterite,
• abs_resin,
• water_surface,
• food_package,
• gutter,
• tin_oxide,
• transistor_elements,
• latex,
• conventional_ink,
• quartzite,
• peach_moonstone,
• shoebox,
• black_velvet,
• canvas,
• soy,
• metal_surface,
• stationery,
• ice,
• metal_substrate,
• kitchen_bowls,
• ti,
• stockade_fence,
• copper,
• salivary_gland,
• fucoid_zygote,
• bismuth_halide,
• newspaper,
• aluminium,
• chalcopyrite,
• engine,
• flash,
• smoothie,
• skin,
• nickel_platinum,
• mouse,
• black_lead,
• nickel_oxide,
• drawing,
• silica,
• thermoplastic_elastomer,
• desk_top,
• plate,
• slump_block,
• vinyl,
• inorganic_pigment,
• solar_panel,
• block,
• textile_fabric,
• colloidal_suspension,
• duchess_satin,
• filament,
• pvc_plastic,
• wool,
• water_body,
• velvet,
• fluorite,
• beer_container,
• bulk_metal,
• surgical_towel,
• nonfat_milk,
• blood,
• water,
• opaque_surface,
• magnetite,
• eggshell,
• lime,
• limonite,
• diamond,
• chocolate,
• tooth,
• insulation_material,
• mirror,
• density_difference,
• eyes,
• card,
• cover,
• check,
• natural_rock,
• towel,
• mica,
• similar_material,
• denim,
• glass_windows,
• rutile,
• quartz,
• aluminum,
• typewriter_key,
• existing_print,
• ceramic_substrate,
• sand,
• styrofoam,
• metal_pipe,
• blackbody,
• cup,
• metallic_paint,
• black_carbon,
• chrome_cr,
• mammalian_tissue,
• bus_electrode,
• lacquer,
• hematite,
• shade_cloth,
• black_paint,
• tungsten_silicide,
• human_skin,
• fence,
• curtain,
• car,
• al_alloy,
• foam,
• platinum,
• view,
• tongue,
• cell_suspension,
• english,
• solid,
• amethyst,
• fluoride,
• coral,
• detergent_bottle,
• brain,
• picture,
• small_model,
• cardboard_box,
• packed_bed,
• digestive_organs,
• polymer,
• meteoritic_iron,
• ceramic_vase,
• bowl,
• whole_grain,
• chrome,
• fabric,
• solid_wall,
• ta,
• foot,
• pigment,
• concrete,
• opaque_ruby,
• vinyl_paint,
• liquid_metal,
• matchbox,
• door,
• polished_silver,
• ore,
• white_card,
• screen_display,
• flower,
• filter,
• eye_sclera,
• brine,
• colored_acrylic,
• silica_fiber,
• granular_medium,
• pillbox_set,
• polyester,
• al,
• shell,
• perfect_blackbody,
• bristol_board,
• zinc,
• video,
• ground,
• box,
• pencil,
• crystalline_polymer,
• document,
• taffeta,
• arsenopyrite,
• chromium,
• vase,
• metal_fabric,
• pvc,
• container,
• carbon,
• ilmenite,
• wall_board,
• tropical_juice,
• ni,
• metal_plate,
• audio,
• fossil,
• sun,
• backpack,
• yogurt_container,
• md,
• mineral,
• magnetic_fluid,
• calculator,
• juice,
• brick_wall,
• bone,
• snow,
• design,
• tin,
• aluminium_bag,
• human_tissue,
• purse,
• eyeglasses,
• soymilk,
• ammo,
• amphibian_egg,
• metallic_conductor,
• human_finger,
• acrylic,
• guts,
• painted_surface,
• pyrite,
• metal_alloy,
• pet,
• lead_letters,
• book,
• dirt,
• black_primer,
• crystal,
• building_partition,
• dentin,
• cr,
• reflector_sheet,
• articular_cartilage,
• exterior_wall,
• cloud_top,
• silicon_wafer,
• enamel,
• metallic_ink,
• alumina,
• oxidized_sulfide,
• dense_gas,
• insect,
• grease,
• breast,
• bloodstone,
• building,
• rock,
• zinc_cream,
• clothing,
• shadow,
• fresh_water,
• soot,
• lead,
• glass_sheet,
• metallic_material,
• marble_dust,
• cloud,
• plasterboard_ceiling,
• film_footage,
• cork,
• steel,
• leaf,
• sawdust,
• granite,
• epoxy,
• flexible_canvas,
• insulator,
• suitable_ink,
• oil,
• chalcedony,
• chalk-dust_whiting,
• silver,
• si,
• silicon_substrate,
• galena,
• denture,
• black_liquor,
• diorite,
• carbon_fibre,
• leg,
• cheese,
• transmission,
• gouache,
• book_page,
• smoky_quartz,
• road,
• briefcase,
• moonstone,
• masonry_wall,
• communicator,
• ag,
• felt,
• key,
• silicon,
• bismuth,
• dense_cloud,
• data_type,
• roof,
• si_wafer,
• carbon_particle,
• phosphate_mineral,
• small_rock,
• oxide,
• image,
• animal_hide,
• agate,
• cr_film,
• urethane_adhesive,
• plaster,
• cushion,
• synthetic-fiber_material,
• red_jasper,
• elastomer,
• alpaca,
• sandwich_bag,
• brick,
• file,
• magnesium,
• weathered_wood,
• plastered_wall,
• statue,
• molten_metal,
• abs,
• suitcase,
• porous_rock,
• partition,
• human,
• locker,
• ebonite,
• fish,
• surgical_instrument,
• natural_rubber,
• chrome_orange,
• mineral_specimen,
• aircraft_canopy,
• sulphide,
• coating_colors,
• liquid_acrylic,
• semiconductor,
• cotton,
• cement,
• suspension,
• fiber,
• semiconductor_wafer,
• tissue,
• tree,
• material,
• alloy,
• marble,
• soil,
• air_photo,
• blue_chalcedony,
• liver,
• porous_plaster,
• beer,
• dust,
• calico_sheet,
• dark_mirror,
• polished_wood,
• sphalerite,
• black_matrix,
• bones,
• ferric_chloride,
• cloth,
• photograph,
• heavy_cloth,
• bag,
• powder,
• reflecting_surface,
• film_canister,
• lead_glove,
• transparent_fluid,
• medical_device,
• thick_papers,
• desk,
• heavyweight_silk,
• translucent_coating,
• plastic,
• mo,
• plastic_bottle,
• page,
• sheet,
• tungsten,
• painted_metal,
• apple,
• planet,
• ceiling,
• handbag,
• brown_glass,
• manganese_oxide,
• computer_chassis,
• table_top,
• barium,
• polymer_substance,
• tower,
• iron,
• tempera,
• rayon,
• mercury,
• liquid,
• red_muscle,
• carved_stone,
• metal_film,
• background,
• invar,
• cu,
• scissors,
• linen,
• gray,
• rib,
• wheat-flour_dough,
• silken_plaster,
• absorption_pad,
• solvent,
• cellular_suspension,
• package,
• cellular_membrane,
• silicone,
• hill,
• gold,
• stibnite,
• goethite,
• foam_sheet,
• sulfide,
• large_building,
• cast_concrete,
• rubber,
• uranium,
• star,
• focusing_cloth,
• glass,
• fiberglass_sheet,
• cobalt_oxide,
• metallic_particle,
• hematite_cement,
• accretion_disk,
• papers,
• bus,
• light,
• floor,
• enamelware_bowl,
• wolframite,
• smoke,
• screen,
• string,
• x-ray_picture,
• medicine_package,
• hand,
• black_onyx,
• common_papers,
• metal_particle,
• cardboard,
• colored_tissue,
• clear_glass,
• silk,
• asphalt_shingle,
• plan,
• tissue_part,
• table,
• carbon_fiber,
• mineral_oxide,
• pulp,
• plastic_cloth,
• videotape,
• garment,
• fe_sulfide,
• ceramic_bowl,
• surgical_clip,
• moon,
• sunken_vessel,
• trash,
• stainless_material,
• tire,