wind vane vs mechanical device

wind vane and mechanical device both are nouns.

Word	Noun	Adjective	Verb	Adverb
wind vane	Yes	No	No	No
mechanical device	Yes	No	No	No

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

wind vane: mechanical device attached to an elevated structure; rotates freely to show the direction of the wind
mechanical device: mechanism consisting of a device that works on mechanical principles

wind vane (noun)	mechanical device (noun)
mechanical device attached to an elevated structure; rotates freely to show the direction of the wind	mechanism consisting of a device that works on mechanical principles