Yours, Etc.: Origins and Uses of 8 Sign-Offs
late 13c. as a term in common law, in Anglo-French, from Old French felonie (12c.) "wickedness, evil, treachery, perfidy, crime, cruelty, sin," from Gallo-Romance *fellonia, from fellonem (see felon).
A grave crime, such as murder, rape, or burglary, that is punishable by death (see capital offense) or imprisonment in a state or federal facility.