Simple categories matching gradual:

• process,
• mechanism,

Members with property gradual:

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