Definition of fettler:
(n) :
A person who maintains railway lines.
(n) :
Someone whose job is to sand and grind small imperfections from metal and ceramic castings.
(n) :
(by extension) Someone who fiddles or tinkers with things.
(n) :
(slang, UK, Lancashire) A friend or mate.
(n) :
(mining, historical) An ostler; one who looks after the horses in a mine.