The Collaborative International Dictionary of English v.0.48:

Felon \Fel"on\, n. [OE., adj., cruel, n., villain, ruffian,
   traitor, whitlow, F. f['e]lon traitor, in OF. also, villain,
   fr. LL. felo. See Fell, a.]
   1. (Law) A person who has committed a felony.
      [1913 Webster]

   2. A person guilty or capable of heinous crime.
      [1913 Webster]

   3. (Med.) A kind of whitlow; a painful imflammation of the
      periosteum of a finger, usually of the last joint.

   Syn: Criminal; convict; malefactor; culprit.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Felon \Fel"on\, a.
   Characteristic of a felon; malignant; fierce; malicious;
   cruel; traitorous; disloyal.
   [1913 Webster]

         Vain shows of love to vail his felon hate. --Pope.
   [1913 Webster]

The Devil's Dictionary (1881-1906):

FELON, n.  A person of greater enterprise than discretion, who in
embracing an opportunity has formed an unfortunate attachment.


Moby Thesaurus II by Grady Ward, 1.0:

96 Moby Thesaurus words for "felon":
   Judas, abscess, aposteme, bad person, bed sore, betrayer, blain,
   bleb, blister, boil, bubo, bulla, bunion, canker, canker sore,
   carbuncle, chancre, chancroid, chilblain, cold sore, convict,
   criminal, crook, culprit, deceiver, delinquent, desperado,
   desperate criminal, double-dealer, eschar, evildoer, fester,
   festering, fever blister, fistula, fugitive, furuncle, furunculus,
   gallows bird, gangster, gaolbird, gathering, gumboil, hemorrhoids,
   jailbird, kibe, lawbreaker, lesion, malefactor, malevolent,
   malfeasant, malfeasor, miscreant, misfeasor, mobster, offender,
   outlaw, papula, papule, paronychia, parulis, petechia, piles,
   pimple, pock, polyp, public enemy, pustule, quisling, racketeer,
   rising, scab, scofflaw, sinner, soft chancre, sore, stigma, sty,
   suppuration, swelling, swindler, traitor, transgressor, tubercle,
   two-timer, ulcer, ulceration, villain, wale, welt, wheal, whelk,
   whitlow, worker of ill, wound, wrongdoer