What is Senior ?
Senior is (adj) 1. older the senior members of the tribe 2. more important, e.g. in rank A sergeant is senior to a corporal. My senior colleagues do not agree with me.(noun) 1. an older person He must be at least ten years your senior. 2. US a student in his or her fourth year or last year at school or college 3. the father in a family where the son has the same name Harry Markovitz Senior
source: Easier English, Student Dictionary Upper Intermediate Level