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]

WordNet (r) 3.0 (2006):

felon
    n 1: someone who has committed a crime or has been legally
         convicted of a crime [syn: criminal, felon, crook,
         outlaw, malefactor]
    2: a purulent infection at the end of a finger or toe in the
       area surrounding the nail [syn: felon, whitlow]

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



Bouvier's Law Dictionary, Revised 6th Ed (1856):

FELON, crimes. One convicted and sentenced for a felony.
     2. A felon is infamous, and cannot fill any office, or become a witness
in any case, unless pardoned, except in cases of absolute necessity, for his
own preservation, and defence; as, for example, an affidavit in relation to
the irregularity of a judgment in a cause in which he is a party. 2 Salk. R.
461; 2 Str. 1148;. Martin's R. 25; Stark. Ev. part 2, tit. Infamy. As to the
effect of a conviction in one state, where the witness is offered in
another, see 17 Mass. R. 515 2 Harr. & McHen. R. 120, 378; 1 Harr. & Johns.
R. 572. As to the effect upon a copartnership by one of the partners
becoming a felon, see 2 Bouv. Inst. n. 1493.



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.