"Beep beep" source (4)

I believe the answer is:

horn

(Other definitions for horn that I've seen before include "Instrument - rhino's feature" , "Warning device on a vehicle" , "Head appendage; warning instrument" , "Brass musical instrument" , "Possession of huntsman or deer" .)

I've seen this clue in the Universal.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.