The term 'Western Union' is associated with two crossword solutions: POSSE (5 letters) and OAS (3 letters). POSSE stands for 'Pursuit of Social and Economic Security for Everyone', which is a non-profit organization that works to improve the economic and social conditions of people in the western United States. OAS stands for 'Organization of American States', which is an international organization composed of 35 member states from North, Central, and South America.