The Collaborative International Dictionary of English v.0.48:

Furuncle \Fu"run*cle\, n. [L. furunculus a petty thief, a boil,
   dim. of fur thief: cf. F. furoncle.] (Med.)
   A superficial, inflammatory tumor, suppurating with a central
   core; a boil.
   [1913 Webster]

WordNet (r) 3.0 (2006):

furuncle
    n 1: a painful sore with a hard core filled with pus [syn:
         boil, furuncle]

Moby Thesaurus II by Grady Ward, 1.0:

76 Moby Thesaurus words for "furuncle":
   abscess, aposteme, bed sore, blain, bleb, blister, boil, bubo,
   bulla, bump, bunion, canker, canker sore, carbuncle, chancre,
   chancroid, chilblain, cold sore, corn, cyst, dilatation, dilation,
   distension, edema, eschar, felon, fester, festering, fever blister,
   fistula, furunculus, gathering, gumboil, hemorrhoids, intumescence,
   kibe, lesion, lump, papula, papule, paronychia, parulis, petechia,
   piles, pimple, pock, polyp, pustule, rising, scab, sebaceous cyst,
   soft chancre, sore, stigma, sty, suppuration, swell, swelling,
   swollenness, tubercle, tumefaction, tumescence, tumidity, tumor,
   turgescence, turgescency, turgidity, ulcer, ulceration, wale, welt,
   wen, wheal, whelk, whitlow, wound