For a die in board games, there is the word ĵetkubo. However not all dice are cubes, since 16-sided or 32-sided dice exist. What do you call these kinds of dice?
This translation of the rules of D&D just calls them for example 20-flanka kubeto. I guess they decided to ignore the inconsistency because if they made a word without kub- in it it would be harder to understand.
In English it is common to use abbreviations like d20 and this rulebook seems to use k20.
First thing coming to mind for me is 32-flanka ĵetkubo.
Otherwise, possibly...32-surfaca ĵetkubo?
Edit: Ah, I see, you mean using something other than "kubo". I'll edit this again after thinking about that.
Edit: pluredro is the word for "polyhedron", so perhaps 32-flanka ĵetpluredro (or ludpluredro?) is going to be a more accurate option. But I don't think people would become terribly confused by the word ĵetkubo plus the number of sides it has, since the intention of that is (probably) easily understood even if it's not quite logical. People probably aren't as familiar with the word pluredro.