Idioms with 'U'

Under the weather: ill; sick; unwell.
"Ted was feeling under the weather yesterday, so he decided not to go to work."

Until hell freezes over: forever.
"Chris can practice the piano until hell freezes over, but he'll never play well because he's tone-deaf."
Note: This expression is used to describe something that will not
change, no matter how long or how often it's done.

Until you're blue in the face: forever.
"You can talk until you're blue in the face, but I won't change my mind."
Note: This expression is used in the same way as "until hell freezes over."

Update: make current; add information to show what has happened recently.
"I need to update my résumé. It doesn't show what I've done during the last year."

Upside down: with the bottom part on top and the top part on bottom.
"Put the glasses upside down in the dishwasher. If you don't do that,
they'll fill with water and you'll have to dry them by hand."

Used to (+ V): an action that was true in the past but is not true now.
"Jane used to live in Austin, Texas. She lives in San Francisco now."