company union vs trade union

company union and trade union both are nouns.

Word	Noun	Adjective	Verb	Adverb
company union	Yes	No	No	No
trade union	Yes	No	No	No

As nouns, trade union is a hypernym of company union; that is, trade union is a word with a broader meaning than company union:

company union: a union of workers for a single company; a union not affiliated with a larger union
trade union: an organization of employees formed to bargain with the employer

Other hypernyms of company union include brotherhood, labor union, trades union, union.

company union (noun)	trade union (noun)
a union of workers for a single company; a union not affiliated with a larger union	an organization of employees formed to bargain with the employer