Ubu
Udi
Udo
Uglier
Ugly
Ugly Cat Joe
Ugly-Bugly
UH
Uhura (after the female character in Star Trek)
Uki
Ulian
Ulla
Ultimate
Ultimate Kitty
Ultimate Warrior
Ultra
Ultra Sonic
Ultra Sound
Ultraviolet
Ulysses
Uma
Umbra
Umgow (after the old Tarzan movie word which meant anything)
Umgowa
Umi
Umma (Turkish for “hope”)
Umpa Lumpa
Unagi
Unbee
Unbelievable
Uncle Buster
Uncle Charles
Uncle Charles Willoughby
Uncle Charlie
Uncle Eeker
Uncle Fester
Uncle Pee
Uncommon
Under My Foot
Under My Thumb
Underdog
Underfoot
Undun
Unicat
Unicorn
Unique
United Kittydom
Unity
Uno Emily
Unusual
Unusual Suspect
Upside Down Kitty
Upton
Uranium
Uranus
Urban
Urchin
Urgent
Urrp (Purr inside-out, or for audiophiles, it’s an out of phase purr)
Ursa Major
Ursa Minor
Ursula
Useless
Usher
Ushki
Ushki (Russian for “ears”)
Usual
Usual Suspect
Usually
Usul
Utopia
Uwe
Uzee
Uzi
Uzo