ratchet vs mechanical device

ratchet and mechanical device both are nouns.

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

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

ratchet: mechanical device consisting of a toothed wheel or rack engaged with a pawl that permits it to move in only one direction
mechanical device: mechanism consisting of a device that works on mechanical principles

ratchet (noun)	mechanical device (noun)
mechanical device consisting of a toothed wheel or rack engaged with a pawl that permits it to move in only one direction	mechanism consisting of a device that works on mechanical principles

ratchet (verb)	mechanical device (verb)
move by degrees in one direction only