The phrase "bring up rear" implies being at the end of a group or movement. To describe the opposite of this, there are antonyms like "lead," "guide," and "front." These terms suggest being at the forefront of a group, taking charge, and leading the way. Other antonyms could include "initiate," "pioneer," and "trailblaze." These words imply being a trendsetter or innovator, setting the pace for others to follow. Additionally, antonyms like "advance," "progress," and "proceed" suggest moving forward and making strides, whereas "bring up rear" implies lagging behind.