Major on Definition 1 of 2Pro Tip 1/3Academic Focus Used when choosing a primary subject of study in an academic setting. She's planning to major on marine biology. Pro Tip 2/3Deep Dive Implies a deep, thorough exploration of a specific subject area or field. For his thesis, he will major on renewable energy systems. Pro Tip 3/3Professional Path Suggests a focus that may guide one's future career or professional interests. After considering her options, she chose to major on accounting.