Modifiers matching reservoir:

• natural,
• nonliving,
• medical,
• liquid,
• subsurface,
• common,
• home,
• environmental,
• stable,
• vast,
• geological,
• deep,
• underground,
• small,
• external,
• fluid,
• impermeable,
• seasonal,
• biological,
• large,
• simple,
• geophysical,
• local,
• sedimentary,
• geologic,
• traditional,
• mobile,
• internal,

Simple categories matching underground:

• organ,
• development,
• music,
• area,
• structure,
• construction,
• tunnel,
• installation,
• facility,
• obstruction,
• feature,
• vegetable,
• liquid,
• void,
• building,
• container,
• room,
• life,
• formation,
• group,
• material,
• hydrocarbon,
• cavern,
• relic,
• line,
• utility,
• object,
• cistern,
• aquifer,
• service,
• equipment,
• opening,
• shelter,
• place,
• location,
• storage,
• fluid,
• cable,
• enclosure,
• conductor,
• works,
• work,
• band,
• world,
• part,
• plant,
• treasure,
• expanse,
• tank,
• activity,
• improvement,
• excavation,
• stem,
• reservoir,
• space,
• conduit,
• housing,
• pipe,
• harvester,
• obstacle,
• cavity,
• cave,
• system,
• passage,
• item,
• bunker,
• fixture,
• supply,
• fortification,
• pipeline,
• property,
• topic,
• duct,
• pest,
• wealth,
• resource,