Verisimilitude - n. the appearance or semblance of truth, or something, as an assertion, having merely the appearance of truth.
According to the oh-so-wonderful Online Etymology Dictionary, the word comes from Latin verisimilitudo “likeness to truth,” which comes from verus “true” + similis “like, similar”.
Wikipedia has an article about verisimilitude as it applies to writers and actors, but the entry for Stephen Colbert’s Truthiness was much more interesting. With great verisimilitude, Stephen Colbert portrays a character who believes in verisimilitudinous ideas (probably because he relies on truthiness).