The antonyms for the word "un-plumbed" are explored, fathomed, measured, probed, and sounded. These words refer to the depth of something that has been fully understood, examined, and investigated. When something is explored, it is thoroughly examined and investigated, leaving no stone unturned. When it is fathomed, it is fully understood or comprehended intellectually. When it is measured, it is evaluated in terms of size, quantity, or amount. Probed means to investigate or explore something deeply, while sounded means to measure the depth of something with a line, especially with a depth finder. All these antonyms for "un-plumbed" help to express the ideas and concepts that are beyond the surface and allow for the understanding of the depths of things.