Source : Webster's Revised Unabridged Dictionary (1913)

trades union \trades" un`ion\, or Trade union \Trade" un`ion\ .
   An organized combination among workmen for the purpose of
   maintaining their rights, privileges, and interests with
   respect to wages, hours of labor, customs, etc.

Source : WordNet®

trade union
     n : an organization of employees formed to bargain with the
         employer; "you have to join the union in order to get a
         job" [syn: {union}, {labor union}, {trades union}, {brotherhood}]