"condition, state, trim," c.1750, Lancashire dialect, from fettle (v.) "to make ready, arrange" (14c.), perhaps from Old English fetel "a girdle, belt," from Proto-Germanic *fatiloz (cf. German fessel "fetter, chain," Old Norse fetill "strap, brace"), from *fat- "to hold."
fettle fet·tle (fět'l)
Proper or sound condition.
Mental or emotional state; spirits.