"condition, state, trim," c.1750, in a glossary of Lancashire dialect, from northern Middle English fettle (v.) "to make ready, fix, prepare, arrange" (late 14c.), which is of uncertain origin, perhaps akin to Old English fetian "to fetch" (see fetch, v.); perhaps from Old English fetel "a girdle, belt," from Proto-Germanic *fatilaz (cognates: German fessel "fetter, chain," Old Norse fetill "strap, brace"), from PIE *ped- (2) "container" (see vat). Related: Fettler; fettling.