a noisemaker (as at parties or games) that makes a loud noise when you blow through it
"The referee blew his horn to signal the end of the game."
one of the bony outgrowths on the heads of certain ungulates
"The male bull elk used his large antlers, not horns, to fight rivals during mating season."
a noise made by the driver of an automobile to give warning
"The truck driver honked his horn to warn pedestrians that he was turning left."
a high pommel of a Western saddle (usually metal covered with leather)
"The cowboy adjusted his hat after brushing off dust from the horn on his new saddle."
any hard protuberance from the head of an organism that is similar to or suggestive of a horn
"The young rhino developed a small, rough horn on its snout within just a few months."
the material (mostly keratin) that covers the horns of ungulates and forms hooves and claws and nails
"The blacksmith examined the hardened horn on the cow's hoof to see if it was thick enough to withstand winter grazing."
a device having the shape of a horn
"horns at the ends of a new moon"
"the horn of an anvil"
"the cleat had two horns"
an alarm device that makes a loud warning sound
"The ship sounded its horn to warn other vessels of its presence in the foggy harbor."
a brass musical instrument consisting of a conical tube that is coiled into a spiral and played by means of valves
"The trumpeter adjusted his embouchure before blowing into the polished brass horn during the concert."
a device on an automobile for making a warning noise
"The driver honked his horn to warn pedestrians about the approaching car."
A hard growth of keratin that protrudes from the top of the head of certain animals, usually paired.
"The bull lowered its large horns to charge at the fence."
In plain English: A horn is either a hard, curved part on an animal's head used for fighting or showing off, or a loud noise-making device attached to vehicles and buildings.
"The bull charged with its large curved horns lowered toward us."
Usage: Use this word to describe natural bony projections covered in keratin found on cattle, sheep, and similar livestock. Avoid confusing it with a musical instrument or vehicle sound when referring specifically to animal anatomy.
To assault with the horns.
"The bull charged and horned its opponent, driving him backward into the fence."
In plain English: To horn is to make noise by blowing air through your mouth into an instrument with metal tubes and valves that you press down on.
"The car's horn honked loudly when someone cut in front of us on the highway."
Cape Horn, at the southern tip of South America.
"My neighbor, Mr. Horn, waved at me from his driveway yesterday."
A surname.
The word "horn" comes directly from Old English and has remained essentially unchanged in meaning since its earliest use. It traveled into modern English through Middle English without any significant shift in definition or form over the centuries.