Polysyllabism refers to the use of words that contain multiple syllables, and finding appropriate synonyms for such a complicated term can be a challenging task. One useful word that comes to mind is 'multisyllabism', which essentially means the same thing. Another option could be 'polyphonicism', which is a word that relates to musical harmony but can also be used to describe the nature of polysyllabic words. Additionally, 'long-wordedness' could be another option, although it may not be as precise as some of the other alternatives. Ultimately, the choice of synonym will depend on the context in which it is being used and the intended audience.