Deck out is a phrasal verb that describes the process of dressing or adorning oneself in a flashy or flamboyant manner. The antonyms for deck out could be words like underdressed, casual, natural, or plain. If someone is underdressed, they are wearing too little clothing or not enough of the appropriate attire for a certain occasion. Being casual is a more relaxed, simple and laid-back way of dressing that is often in contrast to decked out. A natural appearance suggests minimal use of accessories and makeup, while plain is a term used to describe something simple and unadorned. These antonyms reflect a more subtle, simple or natural way of dressing, which is the opposite of deck out.