Alphabet

An alphabet was a system of letters. The first five letters of the English language alphabet were A, B, C, D, and E; the last eight letters of the alphabet were S, T, V, U, W, X, Y and Z. (TV: The Masque of Mandragora)

While under mental attack by the Mandragora Helix, the Fourth Doctor and Sarah Jane Smith spoke the alphabet backwards to concentrate. (TV: The Masque of Mandragora)

River Song, while unaware of the Twelfth Doctor's identity, threatened to remove their organs in alphabetical order, to which the Doctor facetiously asked "Which alphabet?" (TV: The Husbands of River Song)