- undercutter
- underground dam
- undercompacted zone
- undercut
- undercut etching
- undercutting
- underground corrosion
- underground drainage
- underground flow
- underground labor
- underground lake
- underlay lode
- underlying strata
- undermine
- undersaturation
- undertaking
- underwater exploration
- Underwood chart
- undeveloped
- undeveloped reserves
- undiluted
- uneven fracture
- unevenness
- unexplored area
- unfilled
- unfired
- unglazed
- uniaxial xrystal
- unicellular
- unidirectional flow
- uniflow scavenging
- uniflux tray
- uniform contact
- uniform grade
- uniform mix
- uniformity
- unilarm
- underground survey
- underlay
- underlying kast
- undermining
- underproduction
- underwater
- underwater gravimeter
- undetermined multiplier
- undurated aggregate
- unearth
- unicolour
- unidurated
- unimolecular
- union elbow
- union tee
- unit control
- unit operations
- univalent
- unifining
- union colorimeter
- unit elongation
- unit operation
- unitization
- universal grease
- universal stage
- unkindly lode
- unlawful oil
- unleaded
- unlined
- unload
- unmelted
- unmined coal
- union joint
- uniontown method
- unit charge
- unit cooler
- unit process
- unitary
- unitizatzed land
- unknown losses
- unloading
- unloading rack
- unoil
- unoriented texture
- unoxidizable
- unproductive boring
- unrefined oil
- unreliability
- unrest ground
- unsaturated coefficient
- unsaturated hydrocarbon
- unsaturated vapor
- unscreened
- unplasticized PVC
- unroasted ore
- unsaturate
- unscrewing pipe
- unslaked
- unstable fracture
- unstop
- untied investment
- unworked grease
- unlike