The antonyms for "buttons up" are "unbuttons," "loosens," and "unfastens." Unbuttoning is the process of releasing buttons that keep clothes tight or secure. Conversely, loosening is the act of reducing the tension, restriction, or firmness of an object. For example, if you unbutton your shirt or loosen your belt, you make yourself comfortable. Additionally, unfastening refers to the removal of fasteners or closure systems, such as zippers, buckles or hooks. Therefore, these antonyms provide an opposite meaning to "buttons up," which requires an individual to fasten, tighten or secure an object using buttons.