Modifiers matching opal:

• expensive,
• common,
• synthetic,

Simple categories matching synthetic:

• fabric,
• micronutrient,
• carbon,
• material,
• lacquer,
• polymer,
• fiber,
• antidepressant,
• frame,
• cortisone,
• fibre,
• drug,
• instrument,
• entity,
• progestogen,
• activity,
• solvent,
• sedative,
• solid,
• product,
• work,
• equity,
• stimulant,
• pharmaceutical,
• gem,
• peptide,
• clothes,
• gemstone,
• antagonist,
• cure,
• chemical,
• hydrocarbon,
• medicine,
• opal,
• stone,
• contaminant,
• graphite,
• amphetamine,
• aggregate,
• herbicide,
• flavoring,
• androgen,
• yarn,
• vector,
• plastic,
• document,
• medium,
• mineral,
• polyamide,
• hormone,
• penicillin,
• paint,
• corticosteroid,
• fertilizer,
• enzyme,
• glove,
• particle,
• compound,
• nutrient,
• flooring,
• pigment,
• item,
• abrasive,
• event,
• ligand,
• rope,
• progestin,
• textile,
• surface,
• wig,
• crystal,
• coating,
• diamond,
• substance,
• oil,
• input,
• hallucinogen,
• leather,
• phenomenon,
• component,
• precursor,
• system,
• substrate,
• nature,
• anesthetic,
• wax,
• topaz,
• fluid,
• sweetener,
• intermediate,
• food,
• filament,
• membrane,
• gene,
• gas,
• preservative,
• glucocorticoid,
• adhesive,
• narcotic,
• resin,
• carrier,
• antimicrobial,
• painkiller,
• steroid,
• undergarment,
• latex,
• source,
• fumigant,
• oxide,
• bristle,
• sound,
• insulator,
• glue,
• pianoforte,
• insecticide,
• process,
• agent,
• fuel,
• copolymer,
• unit,
• nsaid,
• object,
• layer,
• ester,
• clothing,
• siding,
• condition,
• equipment,
• lubricant,
• scale,
• thing,
• cloth,
• gum,
• progesterone,
• cosmetic,
• reaction,
• papers,
• foam,
• fleece,
• ingredient,
• anticoagulant,
• fertiliser,
• structure,
• antimalarial,
• opiate,
• oestrogen,
• molecule,
• cortisol,
• agonist,
• pesticide,
• elastomer,
• grease,
• part,
• medication,
• silicate,
• starch,
• antibiotic,
• filler,
• estrogen,
• macromolecule,