The phrase "most billow" is often used to describe something that is flowing or moving in a wave-like motion. There are a variety of synonyms that can be used to describe this concept, including undulating, rippling, surging, rolling, and heaving. Each of these words conveys a slightly different feeling or emphasis, with undulating suggesting a gentle, fluid motion, rippling indicating small, quick waves, surging conveying a forceful and powerful movement, rolling suggesting a smooth and consistent motion, and heaving indicating a more abrupt and uneven flow. Depending on the specific context, one of these synonyms may be more appropriate than the others, but all convey a sense of movement and energy.