- unplasticized
- unpredictable
- unpurified
- unrefined
- unreliable
- unsafe fuel
- unsaturated
- unsaturated bond
- unsaturated compound
- unscrew
- unsealed reservoir
- unslaked lime
- unsmeltable
- unstable
- unsulphonated residue
- unsupported
- up-dip
- upburst
- upgrading shop
- upkeep
- uplifted island
- upper bainite
- upper chord
- upturned strata
- uran-mica
- uraniferous
- uranium oxide
- uranophane
- uranosphaerite
- uranotil
- urea
- ureotelic
- uric
- uroblinogen
- usbakite
- used oil
- useful heat
- useful mineral
- unsorted coal
- unstable compound
- unstable hydrocarbon
- unsteady flow
- unstratified structure
- untested
- untreated sludge
- unused
- unworked penetration
- up-flow
- upcast ventilation
- upper moraine
- upper reach
- upset
- uralitization
- uranium lead
- uranium ocher
- UP resin
- up-swelling
- upcast shaft
- upheaved island
- upkeep cost
- uplift
- uplifted peneplain
- uplifted wall
- upper valve
- upright condenser
- upsetting
- upstream
- upstroke press
- uptake
- uptake shaft
- upthrown block
- upward stroke
- uracil
- uralian stage
- uranide
- uranocircite
- uranothallite
- urazole
- urea adduct
- urea dewaxing
- urgonian stage
- uridine
- uroblin
- useful life
- useful power
- ussingite
- usual standard
- utahwax
- utile
- utilities
- utility unit
- v-belt
- vaalite
- vacancy diffusion
- vacancy migration
- vaccination
- vacuum booster
- vacuum column
- vacuum condenser
- vacuum conduction