Etymology: Perhaps < Old French *felon; a 16th cent. quot. in Godefroy s.v. has felons apparently corresponding to ulceribus in the Latin original; but the translation is loose, and the word may mean ‘cholera’, as in Cotgrave; compare quot. ?c1116 at sense 1a below. The sense is consistent with derivation < Latin fell- , fel gall; see felon adj. and n.¹

Etymology: < Old French felon, adjective and noun = Provençal felon , felhon , fellon , adjective, Spanish fellon , Italian fellone , adjective and noun < vulgar Latin *fellōn-em . From its formation, the word must have been originally a noun, fel ( < ˈfello ), whence fell adj.¹, being the subject case, and felon ( < feˈllōn- ) the object case; but so far as documentary evidence goes, both forms were indiscriminately used in Old French as adjective, and the recorded substantive use of the latter is derivative. The curious English form felouns adjective may perhaps be due (like fiers fierce n.) to the -s of the nominative case in Old French (in this instance a product of analogy). The ultimate etymology is uncertain. Of the many conjectures proposed the most probable is that fellōne-m is a derivative of Latin fell- , fel gall, the original sense being ‘one who, or something which, is full of bitterness’ (or ‘venom’, the two notions, as many linguistic facts show, being closely associated in the popular mind). In support of this view it may be pointed out that the noun has had the senses of ‘an envenomed sore’ and ‘cholera’ (see felon n.²); moreover, this etymology accounts perfectly for the strangely divergent senses which the adjective has in the Romance languages: ‘wicked’, ‘angry’, ‘brave’, ‘melancholy, sad’ (Italian fellone), ‘intensely painful’. Of the other suggestions that have been made the most plausible is perhaps that of Prof. R. Atkinson of Dublin, that fello was originally a term of obscene abuse, < Latin fellāre as used in a peculiar sense by Martial and Catullus. Some scholars think that fello is from Old High German *fillo, an unrecorded derivative of fillen to scourge (compare medieval Latin fillo rascal); others have sought to connect it with the obscure second element in the Old English words wælfel ( < wæl carnage; occurring only once, as an epithet of the raven) and ælfæle, ealfelo (usually supposed to be < eal all; only twice, as an epithet of áttor poison). The modern Danish fæl horrible, disgusting, has also been compared; the Middle Dutch fel is adopted < French. The Celtic words often cited are out of the question; the Old French word cannot have come from Wales or Ireland, and Gaulish appears not to have possessed the sound f; the Welsh ff and the Irish f do not correspond etymologically.