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.

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.

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.

4. To wear a costume. My daughter plans to dress up as Cinderella for Halloween.

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.

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.

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?