The term "stump speaker" refers to a person who delivers impromptu speeches in public places, often standing on a stump or other elevated object for visibility. If you're looking for synonyms to describe this type of speaker, here are a few options: soapbox orator, street preacher, sidewalk philosopher, public declaimer, orator of the masses, outdoor public speaker, public haranguer, or impromptu orator. These terms all suggest someone who is unafraid to speak their mind to anyone who will listen, and who is passionate about their message. Whether you agree with them or not, stump speakers have historically played an important role in public discourse and activism.