- Udall
- Nicholas
- Under par
- Under the thumb
- Under your hat
- Under the auspices of
- Under wraps
- underway
- Uneasy lies the head that wears a crown
- Union Jack
- unkindest cut of all
- Until the cows come home
- unwashed
- Up a blind alley
- Up a gum tree
- Up in arms
- Up s*** creek without a paddle
- Up the apples and pears
- Up the duff
- Up the pole
- Up the wooden hill to Bedfordshire
- Up to snuff
- Upper crust
- Upper hand
- Up in arms
- Ups-a-daisy
- Upset the apple-cart
- Upside down
- Up the ante
- Urban myth
- Use your loaf
- Usual suspects
- Using a sledgehammer to crack a nut
- Valentine's Day Poems and Sayings
- Van surfing
- Vanish into thin air
- Veg out
- Verbosity leads to unclear, inarticulate things
- Vice versa
- Vicious circle
- Vis-a-vis
- Visit the ladies' room
- Vorsprung Durch Technik