“The attempt to derive felonia from fel ‘poison’ is merely a folk etymology which came into vogue when ‘felony’ meant a serious crime, and differed from treason. The word was well established in Feudal Law as the characteristic offense against the Feudal relationship. It will hardly do, therefore, to try to determine its meaning merely by reference to English usage ….” Max Radin, Handbook of Anglo-American Legal History 148 n.7 (1936).
felonia
felonia (f[schwa]-loh-nee-[schwa]). [Latin “felony”] Hist. An offense that results in a vassal’s forfeiting his fee.