uncrossed - ussingite
- underset
- underset current
- undershooting of obstructions
- underside
- undersize
- undersize product
- undersluice
- undersoil
- undersurface
- undersurveying
- undertamping
- underthrow
- underthrust
- underthrust fold
- underthrusting
- undertow
- undertow current
- undervibration
- underviewer
- underwall
- underwashing
- underwater
- underwater accumulation
- underwater body
- underwater depression
- underwater energy source
- underwater explosion
- underwater listening post
- underwater operations
- underwater sound
- underwater trough
- underwater volcanicity
- underway
- underwent little diagenetic transformation
- underworked seam
- underworking
- underworking seam
- underworld
- undesirable arrivals
- undesirable energy