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 design of the Globe was related to the 14 stars of the Rexel planetary configuration. (DW: The Shakespeare Code)
 * The Doctor actually uses the adjectival form of this word in the episode.