WordNet sense 1 (a member of the Union Army during the American Civil War):

Federal soldier, Union soldier

WordNet sense 2 (any federal law-enforcement officer):

fed, federal official

WordNet sense 3 (being of or having to do with the northern United States and those loyal to the Union during the American Civil War):

union

WordNet sense 4 (in or characteristic of a region of the United States north of (approximately) the Mason-Dixon line):

northern

WordNet sense 5 (concerned with or applicable to or belonging to an entire nation or country):

national