u ‧ nion ‧ ize BrE AmE ( also unionise British English ) /ˈjuːnjənaɪz/ verb [intransitive and transitive]
if workers unionize or are unionized, they become members of a ↑ trade union
—unionized adjective
—unionization /ˌjuːnjənaɪˈzeɪʃ ə n $ -jənə-/ noun [uncountable]