What is the meaning of unionized?

verb

• Recruit for a union or organize into a union.
  • usage: "We don't allow people to come into our plant and try to unionize the workers"
  • synonyms: unionize, unionise
• Form or join a union.
  • usage: "The auto workers decided to unionize"
  • synonyms: unionize, unionise, organize, organise

adjective

• Not converted into ions.
  • synonyms: nonionized, nonionised, unionised, nonionic
• Being a member of or formed into a labor union.
  • usage: "organized labor"; "unionized workers"; "a unionized shop"
  • synonyms: organized, organised, unionised