The Collaborative International Dictionary of English v.0.48:

Hangman \Hang"man\ (h[a^]ng"man), n.; pl. Hangmen (-men).
   One who hangs another; esp., one who makes a business of
   hanging; a public executioner; -- sometimes used as a term of
   reproach, without reference to office. --Shak.
   [1913 Webster]

WordNet (r) 3.0 (2006):

hangman
    n 1: an executioner who hangs the condemned person

The Devil's Dictionary (1881-1906):

HANGMAN, n.  An officer of the law charged with duties of the highest
dignity and utmost gravity, and held in hereditary disesteem by a
populace having a criminal ancestry.  In some of the American States
his functions are now performed by an electrician, as in New Jersey,
where executions by electricity have recently been ordered -- the
first instance known to this lexicographer of anybody questioning the
expediency of hanging Jerseymen.