adj

• (chiefly poetic) Of a person or animal, their actions, thoughts, etc.: brutal, cruel, harsh, heartless; also, evil, wicked.
  "For Courteſies, tho' undeſerv'd and great, / No gratitude in Fellon-minds beget, / As tribute to his VVit, the churl receives the treat."
• (by extension) Of a place: harsh, savage, wild; of a thing: deadly; harmful.
  "He ask'd the VVaves, and ask'd the Fellon vvinds, / VVhat hard miſhap hath doom'd this gentle ſvvain?"
• (obsolete, rare) Obtained through a felony; stolen.
  "Thus hee that conquer’d men, and beaſt moſt cruell, / (VVhoſe greedy pavves, vvith fellon goods vvere found) / Anſvver’d Goliah’s challenge in a duell, / And layd the Giant groveling on the ground: […]"

noun

• (criminal law) A person who has committed a felony (“serious criminal offence”); specifically, one who has been tried and convicted of such a crime.
  "I doe defie thy coniurations: / And doe attach thee as a fellon heere."
• (obsolete) An evil or wicked person; also (by extension) a predatory animal regarded as cruel or wicked.
  "But he, the King of Heav'n, obſcure on high, / Bar'd his red Arm, and launching from the Sky / His vvrithen Bolt, not ſhaking empty Smoak, / Dovvn to the deep Abyſs the flaming Felon ſtrook."

noun

• (pathology, veterinary medicine) A small infected sore; an abscess, a boil; specifically, a whitlow (“infection near or under the cuticle of a fingernail or toenail”).
  "He hev been away from home for a few days, since he's had that felon upon his finger; for a' said, since I can't work I'll have a hollerday."