The phrase "most deepdown" refers to the core or innermost part of someone or something. There are several synonyms that can be used to describe this concept, such as "innermost," "deepest," "core," "central," "essential," and "fundamental." Each of these words carries a similar meaning and can be used interchangeably to describe the most profound and intimate part of something. When trying to convey the sense of something that is deeply ingrained or rooted, any of these synonyms can be employed. By utilizing a variety of descriptive words, a writer can create a more nuanced and textured understanding of the concept they are trying to convey.