While writing the page How to tune a guitar I noticed a strange mistake in my English vocabulary: I always thought that the two-pronged metal device to tune musical instruments was called "pitchfork" in English. I wouldn't have dared to use "tuning fork", thinking that was a sloppy direct translation of Dutch "stemvork" (stemmen = to tune, vork = fork). But today (June 1, 2003), being 48 years old, to my surprise I find that all dictionaries agree that a pitchfork is a farmer's instrument to manipulate hay. No musical senses are listed. The correct English term is "tuning fork".
Google hits confirm this. I find that the tuning fork was invented in 1711 by John Shore. One source adds "who jokingly called it a pitchfork". I suppose this was done as a wordplay with this sense of the word "pitch":
the property of a sound and especially a musical tone that is determined by the frequency of the waves producing it: highness or lowness of sound.(Source: Merriam-Webster 10th edition).
Pitchfork, by the way, says the Concise Oxford Dictionary, was "pickfork" in Middle-English , so it was a fork to pick hay.