(all) dressed up

Dressed very nicely, perhaps more formally than usual. You need to be dressed up for this event tonight—a suit and tie is appropriate. Because I was all dressed up for the birthday party, I was embarrassed when I saw that the other guests were in shorts and T-shirts. Why are you all dressed up today? Are you going out after work?

dress up

1. To dress formally, perhaps more formally than usual. You need to dress up for this event tonight—a suit and tie would be appropriate. I dressed up for the birthday party and was embarrassed to find all of the other guests in shorts and T-shirts. The chairman of the board will be there tonight, so everyone needs to dress up, OK?

2. To wear attire that is appropriate for a specific occasion. It takes the kids forever to get dressed up for hockey practice, what with all the pads and layers of clothes they need to put on. You're dressed up for tennis, I see. I didn't even know you played! A: "I can't go on a hike, I'm not dressed up for that!" B: "Oh, I see now that you're wearing flip-flops."

3. To improve or attempt to improve the appearance of something by decorating or embellishing it. In this usage, a noun or pronoun can be used between "dress" and "up." Don't worry, a fresh coat of paint will dress this room up. Don't try to dress it up, Mom—my crush completely rejected me. Aunt Jane, it's hard to dress up a rejection from your dream school. Scotty's gonna be depressed about it for a while—there's no way around it.

4. To wear a costume. My daughter plans to dress up as Cinderella for Halloween. Just dress up as a cat or something—this Halloween party is just a casual thing. Wait, the teachers were supposed to dress up today too? Dang, what am I going to do?

5. To dress someone or something in a costume. In this usage, a noun or pronoun can be used between "dress" and "up." I have a friend who really enjoys dressing up her dachshund as different historical figures. She practically dresses her daughter up like a porcelain doll! How is that kid supposed to have any fun in ruffly dresses all the time? I'm going to dress my daughter up as Cinderella for Halloween because that's her favorite princess.

6. noun A children's activity that involves dressing up in costumes. In this usage, the phrase is typically hyphenated. Because my girls love to play dress-up, they regularly emerge from the playroom in feather boas and tiaras. I used to love going to my cousins' house because they had a whole chest of clothes for dress-up. We're playing dress-up, Mommy! Here's a wig and a crown for you!

7. adjective Describing an occasion that requires one to dress in formal or fanciful attire. In this usage, the phrase is typically hyphenated. Tonight's dinner is a dress-up event, so be sure to wear a suit and tie. What costume do you think you'll wear to tonight's dress-up party? A: "I want to have a real dress-up dinner party at my new place." B: "Ugh, can't we just hang out in sweats like we usually do?"

*(all) dressed up

dressed in one's best clothes; dressed formally. (*Typically: be ~; get ~; get someone ~.) I really hate to get all dressed up just to go somewhere to eat.