Origins
The word 'felony' carries within it a moral judgment as well as a legal classification. Its root, Old French 'felon,' meant not merely a criminal but a wicked person, a traitor — someone who had broken faith in the most fundamental way. The word entered English in the thirteenth century as part of the Anglo-French legal vocabulary imported after the Norman Conquest, and it designated from the outset the most serious category of crime, those offences for which the penalty was not merely punishment but total legal destruction: forfeiture of land, goods, and life.
The origin of Old French 'felon' is one of the genuinely contested etymologies in medieval French scholarship. The leading candidates are two. The first derives it from Medieval Latin 'fello' or 'fellō' (villain, traitor), which appears in Carolingian documents from the ninth century but whose own antecedents are unclear. One proposed Latin source is 'fel' (gall, bile), the substance associated in ancient and medieval physiology with bitterness, spite, and malice — the felon was someone acting from the worst possible inner state, driven by bile. The PIE root behind 'fel' is *bhel- (swelling, bile), which also produced English 'bile' and possibly 'bale' in the sense of evil or sorrow. The second etymology derives 'felon' from Frankish *fillo or *fillan (to flog, to beat), making the felon originally a person subject to flogging — a common punishment — rather than one defined by inner wickedness. Neither etymology is universally accepted.
In English common law, the category of felony had precise consequences. A person convicted of felony forfeited all their real and personal property to the Crown, was attainted (their blood corrupted so they could neither inherit nor transmit property to heirs), and faced, in most cases, death. These consequences distinguished felony sharply from misdemeanour (a lesser offence involving a fine or short imprisonment) and from treason (which had its own still more severe consequences). The specific crimes classified as felonies at common law included murder, manslaughter, rape, robbery, burglary, arson, and theft above a certain value.
Later History
The forfeiture consequences of felony were progressively abolished in England during the nineteenth century — the Forfeiture Act 1870 ended most property forfeiture — and the formal felony/misdemeanour distinction was abolished in England and Wales by the Criminal Law Act 1967. In the United States, however, the distinction persists and is constitutionally significant: felonies are generally crimes punishable by more than one year of imprisonment, and a felony conviction typically carries long-term collateral consequences including loss of voting rights, exclusion from jury service, and restrictions on firearm ownership.
The adjective 'fell,' meaning fierce, cruel, or savage — surviving today mainly in the set phrase 'one fell swoop,' which comes from Shakespeare's Macbeth — is a direct sibling of 'felony,' both tracing back to Old French 'felon' in its adjectival sense of wicked and cruel. The same word, the same root, one preserved in the legal lexicon and the other in poetic English.