Simple categories matching gradual:

• process,
• mechanism,

Members with property gradual:

• decay,
• erosion,
• landowner_cause,
• worldwide_church,
• small_scale,
• wind,
• glacial_activity,
• glacial_erosion,
• plastic_flow,
• infection,
• painting,
• geographical_isolation,
• natural_selection,
• rain,
• sea_erosion,
• sedimentation,
• grain_growth,