underdress v dress without sufficient warmth She was underdressed for the hiking trip and suffered hypothermia v dress informally and casually On Fridays, employees can underdress Usage(s) An underdress of heavy fleece wool and waterproof canvas is worn inside, the rubber canvas trousers, with pockets, outside. He wasn't about to underdress for the occasion. Synonym(s) dress down Antonym(s) overdress dress_up