Learn Words by Mnemonics: U List

ubiquitous
being everywhere at once.
Example:-
That Christmas "The Little Drummer Boy" seemed ubiquitous : Justin heard the tune everywhere he went.
Mnemonic:-
it pronounces like mosquitoes which are being everywhere.

unfeigned
genuine; not false or hypocritical
Example:-
He showed unfeigned admiration for the performance.
Mnemonic:-
un(not)-feigned(fined): you are left unfined if you are HONEST, and this is a GENUINE fact.

untenable
incapable of being defended or justified
Example:-
His unwavering belief in fundamental creationism is untenable in my opinion. 
Mnemonic:-
a child un(der) ten not able defense himself they need parents maintenance (under+ten+not able)

urbane
sophisticated; refine; elegant
Example:-
Joseph was always overly polite and had kind words for everyone, even when they mistreated him; he was urbane.
Mnemonic:-
People living in urban areas are sophisticated.