V

As spoken by Sarah Jane Smith, V was the twenty-first letter of the alphabet, following T and preceding U. (TV: The Masque of Mandragora)

While binding Chris Cwej's consciousness to the conceptual weapon V-Time, the Surgeon told Cwej that the letter V was, among other things, an ideal representation of the meeting of different points. (PROSE: The V Cwejes)

Behind the scenes
In the real world, V is the twenty-second letter of the alphabet.