In this case "prill" is the obscure word, sorry. I understand some people will be annoyed that the obscure words they happen to know don't work, but I think it's better for the 95% of players who would be disappointed to find that "prill" or "brall" was part of the solution, effectively giving them no chance.

Each puzzle has only one solution, so if you find one that doesn't work with 1 or more extremely uncommon words, it's safe to assume that's not the solution.