stoker vs mechanical device

stoker and mechanical device both are nouns.

Word	Noun	Adjective	Verb	Adverb
stoker	Yes	No	No	No
mechanical device	Yes	No	No	No

As nouns, mechanical device is a hypernym of stoker; that is, mechanical device is a word with a broader meaning than stoker:

stoker: a mechanical device for stoking a furnace
mechanical device: mechanism consisting of a device that works on mechanical principles

stoker (noun)	mechanical device (noun)
a mechanical device for stoking a furnace	mechanism consisting of a device that works on mechanical principles
a laborer who tends fires (as on a coal-fired train or steamship)