| Idiom | Meaning | Example |
| use up | use all of it, use all you have | We've used up all the shampoo. Please buy some more. |
| used to | accustomed to, having felt it often | Lynn is used to being alone. Henry is away from home a lot. |
| useless as a fifth wheel | (See as useless as a fifth wheel) | |
| useless as the tits... | (See as useless as tits on a boar) | |
| user friendly | easy to learn or use, easy to operate | Cars with automatic transmission are user friendly - easy to drive. |
| Uzi | (See pack Uzis) |