The term "under-skirt" typically refers to a skirt or petticoat that is worn underneath another skirt or dress. Some synonyms for this term include slip, petticoat, underskirt, and crinoline. Each of these words describes a type of undergarment that can be worn to add volume or shape to a dress or skirt, or to provide an additional layer of coverage and modesty. While these words are often used interchangeably, there may be subtle differences in how they are constructed or styled. Overall, they all serve a similar purpose and can be a useful addition to any wardrobe.