uncrossed - ussingite
- undercutting jib
- undercutting machine
- underdeveloped
- underdeveloped spores
- underditch
- underdrain
- underdrainage
- underdrilling
- underearth
- underedge
- underexplored
- underexplored area
- underexplored region
- underfeature
- underfit
- underfitness
- underflow
- underflow conduit
- underflow pump
- underfold
- underfoot
- underframe
- underground
- underground air
- underground bailiff
- underground boring
- underground bunker
- underground cauldron subsidence
- underground center
- underground conditions
- underground crew
- underground dam
- underground development of ore deposits
- underground drainage
- underground equipment
- underground excavations
- underground extraction
- underground fan
- underground feature
- underground flooding