Modifiers matching ground:

• neutral,
• heavy,
• soft,
• clear,
• irregular,
• hard,
• safe,
• dangerous,
• good,
• difficult,
• rocky,
• over,
• loose,
• rough,
• high,
• sandy,
• unstable,
• vertical,
• level,
• natural,
• mechanical,
• sensitive,
• open,
• softer,
• stable,
• electrical,
• coarse,
• metallic,
• hazardous,
• rigid,
• low,
• sacred,
• moist,
• elevated,
• flat,
• convenient,
• familiar,
• artificial,
• dry,
• permeable,
• barren,
• shiny,
• bad,
• higher,
• routine,
• common,
• wet,
• uncultivated,
• working,
• paved,
• weak,
• unsecured,
• woven,
• new,
• off,
• white,
• firm,
• particular,
• under,
• slippery,
• sized,
• conductive,
• holy,
• disturbed,
• harder,
• private,
• up,
• metal,
• waterlogged,
• technical,
• grown,
• undisturbed,
• porous,
• durable,
• uneven,
• old,
• clean,

Simple categories matching harder:

• material,
• assets,
• feldspar,
• stone,
• wood,
• powder,
• formation,
• mineral,
• surface,
• metal,
• resin,
• genre,
• drug,
• fabric,
• thing,
• particle,
• substance,
• cheese,
• object,
• layer,
• glass,
• tissue,
• alloy,
• ingredient,
• agent,
• work,
• narcotic,
• pin,
• polymer,
• stuff,
• abrasive,
• crystal,
• music,
• part,
• rock,
• gemstone,
• deposit,
• structure,
• sport,
• substrate,
• sediment,
• medium,
• stimulant,
• food,
• filler,
• currency,
• ground,
• aggregate,
• boot,