The term "deck up" is often used to describe dressing up or decorating in a fancy way. However, there are several antonyms for this phrase that denote a more relaxed or casual appearance. For example, "dress down" refers to wearing less formal clothes or removing decorative accessories. Another antonym is "plain," which means unadorned or lacking embellishments. Alternatively, "de-clutter" indicates removing excess items or simplifying a space. "Minimize" conveys reducing the amount of decoration, while "uncover" implies unveiling a simpler or more basic design. These antonyms provide a contrast to the ornate and elaborate sense of "deck up.