ultimus Romanorum (L.), the last of the Romans.
ultra vires (L.), beyond one's powers.
und so weiter (Ger.), or u.s.w., and so forth.
usque ad nauseam (L.), to disgust.
usus loquendi (L.), current usage of speech.
utile dulci (L.), the useful with the agreeable.
ut infra (L.), as below.
ut supra (L.), as above.
vade in pace (L.), go in peace.
vade mecum (L.), go with me: a constant companion.