dissident (adj.)
1530s, from Latin dissidentem (nominative dissidens), present participle of dissidere "to be remote; disagree, be removed from," literally "to sit apart," from dis- "apart" (see dis-) + sedere "to sit" (see sedentary).
dissident (n.)
1766, in reference to Protestants, from dissident (adj.). In the political sense first used 1940, coinciding with the rise of 20c. totalitarian systems, especially with reference to the Soviet Union.