labor union vs brotherhood

labor union and brotherhood both are nouns.

Word	Noun	Adjective	Verb	Adverb
labor union	Yes	No	No	No
brotherhood	Yes	No	No	No

As nouns, labor union and brotherhood are synonyms defined as:

labor union and brotherhood: an organization of employees formed to bargain with the employer

Other synonyms of labor union include trade union, trades union, union.

labor union (noun)	brotherhood (noun)
an organization of employees formed to bargain with the employer	the feeling that men should treat one another like brothers
	people engaged in a particular occupation
	an organization of employees formed to bargain with the employer
	the kinship relation between a male offspring and the siblings