reduction gear vs power train

reduction gear and power train both are nouns.

Word	Noun	Adjective	Verb	Adverb
reduction gear	Yes	No	No	No
power train	Yes	No	No	No

As nouns, power train is a hypernym of reduction gear; that is, power train is a word with a broader meaning than reduction gear:

reduction gear: gearing that reduces an input speed to a slower output speed
power train: wheelwork consisting of a connected set of rotating gears by which force is transmitted or motion or torque is changed

Other hypernyms of reduction gear include gear, gearing, geartrain, train.

reduction gear (noun)	power train (noun)
gearing that reduces an input speed to a slower output speed	wheelwork consisting of a connected set of rotating gears by which force is transmitted or motion or torque is changed