There are several synonyms for the word "loud-speaker" that can be used interchangeably in different contexts. Some of the commonly used synonyms for loud-speaker include PA system, public address system, horn speaker, megaphone, and sound system. PA system and public address system are often used in large events or gatherings where the speaker needs to communicate with a large audience. Horn speaker and megaphone are commonly used for outdoor events or in sports stadiums where the speaker needs to project their voice over a large area. Sound system, on the other hand, is a general term used for any audio equipment that amplifies sound.