pickup arm vs mechanical device

pickup arm and mechanical device both are nouns.

Word	Noun	Adjective	Verb	Adverb
pickup arm	Yes	No	No	No
mechanical device	Yes	No	No	No

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

pickup arm: mechanical device consisting of a light balanced arm that carries the cartridge
mechanical device: mechanism consisting of a device that works on mechanical principles

pickup arm (noun)	mechanical device (noun)
mechanical device consisting of a light balanced arm that carries the cartridge	mechanism consisting of a device that works on mechanical principles