I love V!
Valentine's Day, Veracity, Voluptuous, Vexatious, Victorious, Virtuous, Vicious, Villain. A word nerd's dream.
But a V literary device?
Took a little research, but I found...
The sense that what one reads is "real," or at least realistic and believable. For instance, the reader possesses a sense of verisimilitude when reading a story in which a character cuts his finger, and the finger bleeds. If the character's cut finger had produced sparks of fire rather than blood, the story would not possess verisimilitude. Note that even fantasy novels and science fiction stories that discuss impossible events can have verisimilitude if the reader is able to read them with suspended disbelief. (source)
Verisimilitude is one of the things that makes a good book great. A book is an author's attempt to define truth to the reader. Truth, unlike facts, is in the eye of the beholder. With enough convincing, something that is factually inaccurate can become our truth.
Since a work of fiction is by definition invented in an author's imagination, verisimilitude becomes the ability to create a believable storyline. When doubt creeps in, the "made up" aspects of fiction take root and the reader disengages. Never good.
From my research on the word, the responsibility for verisimilitude use to lie with the audience--what they could accept as truth. Now it seems to refer more to the creator--what they can portray as truth.
Where it's tricky... fantasy and paranormal. An author in these genres must convince the reader that something that is obviously not real (e.g., Narnia) is very real.
What will make you doubt a novel's verisimilitude the quickest? For me, it's when a character I care about suddenly does something completely out of left field. It makes me doubt everything in the book--everything I thought I knew.
Check out some great V posts here.