I think what VSmith was driving at was that many people seeing the name say “mallet” like the thing you use to hit a croquet ball with, with the first syllable rhyming with “pal” as in your friend, and the last syllable sounding like the word “let”.
The correct pronounciation would be more like “Mall-LAY”…“Mall” like shopping mall, “lay” like lay down.
In America we generally say “Mal-lee” - “Mal” like ‘pal’ and “lee” like the name Lee.
Just to stir the pot a little more, back to the original question, a Mallet is generally defined as a steam engine having two sets of drivers, where the first set of drivers are articulated so they can turn separately from the rest of the engine, and that uses steam in a compound set-up with high and low pressure cylinders. Articulated engines that use high pressure steam directly to all four cylinders were often called “simplified” or “simplex” articulateds.
BTW a little off subject but it’s become popular in science programs on TV and such to pronounce “Halley” from Edmund Halley of Halley’s Comet fame as “Hal-lee” with the “Hal” sounding like the name Hal. This is wrong; back in 1986 the BBC visited Edmund Halley’s descendents who still live in the same country estate in England, and the family explained it was “Hall-lee” with the “Hall” pronounced just like the word hall or as in “hallway”. [swg]