Most furrowed refers to the state of something that has the deepest or most pronounced furrows. Its antonyms would be words that describe the opposite, such as smooth, unlined, flat, and even. These terms could be used to describe a surface that is not furrowed or grooved, such as a freshly paved road or a calm lake. Alternately, a surface that is only slightly furrowed or wrinkled could be called shallow or smooth. In essence, any word or phrase that describes a surface without deep, noticeable grooves or furrows could be considered an antonym for "most furrowed.