S: (n) union, sum, join (a set containing all and only the members of two or more given sets) "let C be the union of the sets A and B"
Verb
S: (v) join, fall in, get together (become part of; become a member of a group or organization) "He joined the Communist Party as a young man"
S: (v) join (cause to become joined or linked) "join these two parts so that they fit together"
S: (v) join (come into the company of) "She joined him for a drink"
S: (v) join, conjoin (make contact or come together) "The two roads join here"
S: (v) connect, link, link up, join, unite (be or become joined or united or linked) "The two streets connect to become a highway"; "Our paths joined"; "The travelers linked up again at the airport"