Definitions for "foghorn"
A horn that emits a loud low-pitched sound, used on ships navigating in a fog, to warn other ships of their presence.
A noise signal used before electronic equipment was developed, used to warn ships when they were coming in too close to shore in a thick fog. They could be hand-held, making use of bellows that took in air and pushed it out through a loud horn.
a loud low warning signal that can be heard by fog-bound ships