When Mary (later Queen of Scots) went to France as a young girl (for education & survival), Louis, King of France, learned that she loved the Scottish game 'golf.' We are told that he had the first golf course outside of Scotland built for her enjoyment.
To make sure she was properly chaperoned (and guarded) while she played, Louis hired cadets from a military school to accompany her. Mary liked this a lot and when she returned to Scotland (not a very good idea in the long run), she took the practice with her. In French, the word cadet is pronounced 'ca-day' and the Scots changed it to 'caddie.'