When it comes to describing something as "most constructural," there are a few synonyms you could use to convey a similar meaning. For example, you might describe something as being the most foundational, essential, or fundamental piece of a particular structure. Alternatively, you could use words like pivotal, crucial, or critical to emphasize its importance. Another option might be to describe something as the most integral or central part of a design, or as the key component that holds everything together. Ultimately, the choice of synonym will depend on the context in which you are using the word, as well as the nuances of meaning you wish to convey.