WordNet sense 1 (the state of being joined or united or linked):

unification

WordNet sense 2 (the state of being a married couple voluntarily joined for life (or until divorce)):

marriage, matrimony, wedlock, spousal relationship

WordNet sense 3 (healing process involving the growing together of the edges of a wound or the growing together of broken bones):

conglutination

WordNet sense 4 (the United States (especially the northern states during the American Civil War)):

north

WordNet sense 5 (an organization of employees formed to bargain with the employer):

brotherhood, labor union, trades union

WordNet sense 6 (a set containing all and only the members of two or more given sets):

join, sum

WordNet sense 7 (being of or having to do with the northern United States and those loyal to the Union during the American Civil War):

federal

WordNet sense 8 (in or characteristic of a region of the United States north of (approximately) the Mason-Dixon line):

northern

WordNet sense 9 (the act of pairing a male and female for reproductive purposes):

conjugation, coupling, mating, pairing, sexual union

WordNet sense 10 (the act of making or becoming a single unit):

jointure, uniting