The phrase "drop down" can be substituted with various synonyms depending on the context. The phrase could be replaced with "collapse," which indicates a sudden downward movement or failure. "Descend" or "fall" are appropriate synonyms when referring to a reduction in height or position. A "dropdown menu" could also be referred to as a "flyout" or "popout menu" since the menu appears when the user hovers over or clicks on a designated area. In website design, "expandable menu" and "accordion menu" can also be used to describe such menus. Overall, there are various words that can replace "drop down," and the choice of words relies heavily on the context in which they are used.