Public executioner (7)
I believe the answer is:
hangman
'public executioner' is the definition.
(hangman is a kind of public executioner)
This is all the clue.
(Other definitions for hangman that I've seen before include "Word game - executioner" , "Public executioner like Jack Ketch" , "Killer" , "wordgame?" , "Word-guessing game - executioner" .)