"Most decagonal" refers to something that has the most number of sides in the shape of a decagon. A decagon is a polygon with ten sides and ten angles. Some synonyms that can be used in place of "most decagonal" are "having the most number of sides in a decagon", "10-sided", "decagonal", "polydecagonal", "decapentagonal", and "ten-angular". These words can be used interchangeably depending on the context, but they all refer to the same concept of something having ten sides in the shape of a decagon. It's important to choose the appropriate synonym based on context, clarity and intended audience.