When it comes to describing "big brother", there are various words one can use to convey the same idea. Some synonyms for big brother include "authority figure", "watchful eye", "overseer", "guardian", "protector", "supervisor", and "mentor". These terms generally refer to someone who keeps a close eye on others and has a level of authority or responsibility over them. In a more negative context, big brother can also refer to a person or entity that is excessively controlling and invasive, in which case synonyms could include "intrusive", "domineering", or "oppressive". Overall, the choice of synonym will depend on the context and the specific connotations that fit best.