Sentence:  From a dead stand, with regulator full open and the lever at about 50 per cent we got up to about 60 m.p.h. by the top of the bank. The big <WSD>compound</WSD> was making plenty of noise - but what musical and wonderful noise! 
Meaning of the word marked with <WSD> tags:  a (compound locomotive), a steam locomotive with both high-pressure and low-pressure cylinders.