From The Tommyknockers by Stephen King:
Late last night and the night before, Tommyknockers, Tommyknockers,
knocking at the door. I want to run, don't know if I can, 'cause I'm
so afraid of the Tommyknocker man.
But aside from the slang meaning of knocker(breast), the knocker is really a creature related to mining lore (NED, Century, as follows):
The Knocker, Knacker, Bwca (Welsh), Bucca (Cornish) or Tommyknocker (US)
is a mythical creature in Welsh, Cornish and Devon folklore.–2. A spirit or goblin supposed to dwell in mines, and to indicate the
presence of rich veins of ore by knocking.The miners say the Knocker is some being that inhabits in the concaves and hollows of the Earth, and that it is thus kind to some
men of suitable temper, and directs them to the ore by such this
knocking.Hooson, quoted by R. Hunt in British Mining.
But accounts may vary… The French version of the article discloses that the German Meister Hämmerlinge (maître marteleur) is also a Knocker. And King's Tommyknockers will tell you where to dig, yet their motives may be questionable.
Why is the word prefixed with "tommy" in AmE, where does it come from? Does it mean something different? The word tommy refers either to Thomas Atkins1, or to a diminutive of the name Thomas, a ration, or is related to the truck system i.e. the tommy would be the wager paid in goods instead of money. How is that related, if at all, to the knocker?
1. From the entry: […] a familiar name for the typical private soldier in the British Army; arising out of the casual use of this name in the specimen forms given in the official regulations from 1815 onward. […] Now more popularly Tommy Atkins or Tommy […]. From wikipedia on the name Thomas: based on the Biblical Greek Θωμᾶς, which is itself a transcription of the Aramaic te'oma תאומא "twin", the Hebrew cognate being tə'ōm תאום.(Reference to citation being required, omitted.)
Best Answer
This is only an assumption, but after doing a bit of research I have come up with the following notations and now believe the "Tommy" in TommyKnockers is a carry over of these references of a "Tommy" being a British person (soldier) in as much as the legend of them correlates in the U.S. mining communities about the same time frame and the high possibility that some of the miners were veterans of WWI. I found it on Wikipedia under the slang term Digger...
"While the Australians and New Zealanders would call each other "Digger", the British tended to call the New Zealanders "Kiwis" and Australians "Diggers". ***
*** from Tommy Atkins then following thru and reviewing Tommy Atkins also on Wiki page...
"Tommy Atkins (often just Tommy) is slang for a common soldier in the British Army. It was already well established in the 19th century, but is particularly associated with World War I. It can be used as a term of reference, or as a form of address. German soldiers would call out to "Tommy" across no man's land if they wished to speak to a British soldier. French and Commonwealth troops would also call British soldiers "Tommies".
So in correlation to the legend of "Knockers" coming to the U.S. by way of Cornish immigrant miners, American miners most likely called the "Knocker's Tommies" meaning that they were British.