Irrefragability is a complex word that refers to the quality of being impossible to refute or deny. Synonyms for irrefragability include invincibility, indisputability, certainty, infallibility, incontrovertibility, and unassailability. These words all describe something that is irrefutable or undeniable, and cannot be argued or disputed. They are often used in academic or legal contexts where a statement or argument must be proven beyond doubt or refute. It is important to note, however, that while these synonyms all convey similar concepts, they may carry slightly different connotations or shades of meaning depending on the context in which they are used.