brotherhood vs labor union

brotherhood and labor union both are nouns.

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

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

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

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

brotherhood (noun)	labor union (noun)
the feeling that men should treat one another like brothers	an organization of employees formed to bargain with the employer
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