On only the rarest occasions do philosophers suggest that some term ("good", "morality," "rationalism", "free will", "soul", "knowledge") might not possess a definition that is precise enough to do the work that we ask of it.

At least when it comes to the concepts "Good," "Morality" and "Free Will," I'm familiar with some fairly prominent suggestions that they are in dire need of redefinition and other attempts to narrow or eliminate discussions about such loose ideas altogether.