Tetradecagon

A tetradecagon was a 14-sided object.

When trying to understand why the Globe Theatre had a tetradecagal design, the Doctor once enlisted the help of Martha Jones and William Shakespeare to find other objects and concepts that were arranged around the number 14 — like sonnets. As it turned out, the tetradcagal shape of the Globe — in fact designed by the Carrionites — was related to the 14 stars of the Rexel planetary configuration. The odd design allowed the Carrionites to turn the theatre into an energy converter, using which they hoped to destroy human life on Earth. (DW: The Shakespeare Code)
 * The Doctor only actually uses the adjectival form of this word in the episode, while Lilith used the noun.