Emily Dickinson Lexicon

FEL'ON, n. [Fr. felon; Low L. felo; Arm. fellon; It. fello or fellone, a thief. I accord with Spelman in deducing this word from the root of fail, the original signification being, a vassal who failed in his fidelity or allegiance to his lord, and committed an offense by which he forfeited his feud. Hence in French, felon is traitorous, rebellious. So the word is explained and deduced in Gregoire's Armoric Dictionary. The derivation from fee and lon in Spelman, copied by Blackstone, is unnatural.]

1. In law, a person who has committed felony. [See Felon.]
2. A whitlow; a painful swelling formed in the periosteum at the end of the finger. Wiseman.