In the English language, there are several synonyms for the word "indefinableness." Some of the most common synonyms for this term include "unfathomable," "inscrutable," "unexplainable," "indescribable," "inexpressible," "unimaginable," "unclear," "enigmatic," "ambiguous," "incomprehensible," "vague," and "mysterious." Depending on the context in which the word is used, one synonym may be more appropriate than another. For example, "unfathomable" and "inscrutable" might be better suited to describe a complex scientific concept, while "enigmatic" and "ambiguous" might be more appropriate to describe an abstract piece of art.