The word "most unplumbed" means that something is the deepest or most profound. Therefore, its antonyms are words that describe something shallow or superficial. These words might include words like superficial, shallow, simple, basic, or uncomplicated. Other words that can be used as antonyms for "most unplumbed" might include words like trivial, conventional, conventional, elementary, or self-evident. The choice of antonym will depend on the context in which it is being used. For example, in a literary context, the antonym for "most unplumbed" might be something like the "banal" or the "uninspired." On the other hand, in a professional or technical context, the antonym might be something like the "routine" or the "straightforward.