Now almost exclusively the role of Susie Dent, the role of lexicographer has traditionally been occupied by a member of the Oxford University Press or a member of the show's production team. On-screen, the lexicographer gives the final decision as to whether a word can be allowed or not. See the list of lexicographers.
The guest celebrities help Susie Dent find the longest words, and occupy a slot which they tell amusing anecdotes, perform anagrams, magic or other tricks, or add general entertainment to the proceedings. At present, this is between rounds 6 and 7. The celebrity is typically credited as 'Special Guest' in the credits roll. See the list of Dictionary Corner guests.