warning device vs horn

warning device and horn both are nouns.

Word	Noun	Adjective	Verb	Adverb
warning device	Yes	No	No	No
horn	Yes	No	Yes	No

As nouns, horn is a hyponym of warning device; that is, horn is a word with a more specific, narrower meaning than warning device:

warning device: a device that signals the occurrence of some undesirable event
horn: a device on an automobile for making a warning noise

Other hyponyms of warning device include automobile horn, car horn, hooter, motor horn, burglar alarm, fire alarm, smoke alarm, siren.

warning device (noun)	horn (noun)
a device that signals the occurrence of some undesirable event	one of the bony outgrowths on the heads of certain ungulates
	any hard protuberance from the head of an organism that is similar to or suggestive of a horn
	a brass musical instrument consisting of a conical tube that is coiled into a spiral and played by means of valves
	a brass musical instrument with a brilliant tone; has a narrow tube and a flared bell and is played by means of valves
	an alarm device that makes a loud warning sound
	a high pommel of a Western saddle (usually metal covered with leather)
	a device on an automobile for making a warning noise
	a noisemaker (as at parties or games) that makes a loud noise when you blow through it
	a device having the shape of a horn
	a noise made by the driver of an automobile to give warning
	the material (mostly keratin) that covers the horns of ungulates and forms hooves and claws and nails

warning device (verb)	horn (verb)
	stab or pierce with a horn or tusk