General condition or state of health and spirits (noun); to clean, repair, or put in good condition (verb). 'In fine fettle' means in excellent condition.
From Old English 'fetel' meaning straps or equipment. The word evolved to mean the overall arrangement or 'fit' of something, and later extended to mean condition or state of being. By the 1800s it was commonly used to describe someone's health.
Yorkshire and Northern England miners developed 'fettle' into their own vocabulary—'fettling' their coal mine equipment became so specialized that the word is still used by metalworkers today. It's a perfect example of regional dialect becoming technical jargon!
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