Ubiquitous (adj) being everywhere at the same time

Personal computer, once a rarity, have become ubiquitous.

 

Unconscionable ( adj) not controlled by conscience, unscrupulous

Stealing money from every citizen of that town was unconscionable. He should be ashamed of himself for doing it.

Unctuous ( adj) oily, both literally and figuratively, insincere

Salad oil is literally unctuous

Uniform( adj) consistent; unchanging; the same for everyone

Traffic laws are similar form one state to the next, but they are not uniform.

Unremitting (adj): unceasing, unabated, relentless

Superman waged an unremitting battle against evildoers everywhere.

Unwitting ( adj): unintentional; ignorant; not aware

 

Urbane (adj) : poised, sophisticated; refined

The new magazine was far too urbane to appeal to a wide audience outside the big city.

Usurp (v): to seize wrongfully

The founder’s scheming young nephew usurped a position of power in the company.

Utilitarian (adj) stressing usefulness or utility above all other qualities, pragmatic

 

Utopia (n). an ideal society

A country where nobody had to work would be Quentin’s idea of utopia.

Such plans or expectations are utopian plans or expectations. ( unrealistic or impractical plans by someone )

Opposite: Dystopia