Nouns

(n)union, labor union, trade union, trades union, brotherhoodan organization of employees formed to bargain with the employer“you have to join the union in order to get a job”
(n)coupling, mating, pairing, conjugation, union, sexual unionthe act of pairing a male and female for reproductive purposes“the casual couplings of adolescents”, “the mating of some species occurs only in the spring”
(n)union, unificationthe state of being joined or united or linked“there is strength in union”
(n)marriage, matrimony, union, spousal relationship, wedlockthe state of being a married couple voluntarily joined for life (or until divorce)“a long and happy marriage”, “God bless this union”
(n)union, conglutinationhealing process involving the growing together of the edges of a wound or the growing together of broken bones
(n)uniona political unit formed from previously independent people or organizations“the Soviet Union”
(n)union, sum, joina set containing all and only the members of two or more given sets“let C be the union of the sets A and B”
(n)unionthe occurrence of a uniting of separate parts“lightning produced an unusual union of the metals”
(n)uniona device on a national flag emblematic of the union of two or more sovereignties (typically in the upper inner corner)
(n)union, unification, uniting, conjugation, jointurethe act of making or becoming a single unit“the union of opposing factions”, “he looked forward to the unification of his family for the holidays”

Adjectives

(a)unionof trade unions“the union movement”, “union negotiations”, “a union-shop clause in the contract”