Which word best fits the definition of "incontrovertible"?

The term "incontrovertible" refers to something that is undeniable or indisputable; it is used to describe facts or evidence that cannot be contradicted or challenged. Therefore, the word "undeniable" aligns perfectly with this definition, as it suggests that something is so clear and evident that it cannot be reasonably questioned or disputed.

In contrast, the other options do not fit the context of "incontrovertible." "Definable" suggests that something can be clearly defined or outlined, but it does not imply anything about its validity or certainty. "Questionable" implies that something may be doubted or is uncertain, which directly opposes the meaning of "incontrovertible." Finally, "ambiguous" relates to something that is unclear or open to more than one interpretation, again contrasting with the idea of undeniable certainty. Thus, "undeniable" is the only word that accurately encapsulates the meaning of "incontrovertible."